diff --git a/NEWS.md b/NEWS.md
index ee60e7806f..5a7785f643 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -14,6 +14,12 @@ target range. (#2571)
 - Update `ADEG` template to flag `ABLFL` and `ANL01FL` based on `DTYPE == "AVERAGE"` records. (#2561)
 
 ## Updates of Existing Functions
+- added `"message"` as option for `check_type` argument in `filter_extreme()` function. (#2481)
+
+- Users can now specify how duplicate records are handled in `derive_param_tte()` using the `check_type` argument, with options including `"error"`, `"warning"`, `"message"`, or `"none"`, allowing for greater flexibility in managing duplicate data scenarios. (#2481)
+  
+- `order` argument has been added to `event_source()` and `censor_source()` and  
+  defaulted to `NULL` to allow specifying variables in addition to the date variable. This can be used to ensure the uniqueness of the select records if there is more than one record per date.  (#2481)  
 
 - NCICTCAEv5 grading criteria (`atoxgr_criteria_ctcv5`):
 
diff --git a/R/derive_merged.R b/R/derive_merged.R
index d32e8089f0..64e166b2d8 100644
--- a/R/derive_merged.R
+++ b/R/derive_merged.R
@@ -112,15 +112,15 @@
 #'
 #' @param check_type Check uniqueness?
 #'
-#'   If `"warning"` or `"error"` is specified, the specified message is issued
+#'   If `"warning"`, `"message"`, or `"error"` is specified, the specified message is issued
 #'   if the observations of the (restricted) additional dataset are not unique
 #'   with respect to the by variables and the order.
 #'
 #'   If the `order` argument is not specified, the `check_type` argument is ignored:
-#'    if the observations of the (restricted) additional dataset are not unique with respect
-#'    to the by variables, an error is issued.
+#'   if the observations of the (restricted) additional dataset are not unique with respect
+#'   to the by variables, an error is issued.
 #'
-#'   *Permitted Values*: `"none"`, `"warning"`, `"error"`
+#'   *Permitted Values*: `"none"`, `"message"`, `"warning"`, `"error"`
 #'
 #' @param duplicate_msg Message of unique check
 #'
diff --git a/R/derive_param_tte.R b/R/derive_param_tte.R
index daa9f9af4d..84eee1f5a6 100644
--- a/R/derive_param_tte.R
+++ b/R/derive_param_tte.R
@@ -60,6 +60,15 @@
 #'
 #'   A list of symbols created using `exprs()` is expected.
 #'
+#' @param check_type Check uniqueness
+#'
+#'   If `"warning"`, `"message"`, or `"error"` is specified, the specified message is issued
+#'   if the observations of the source datasets are not unique with respect to the
+#'   by variables and the date and order specified in the `event_source()` and
+#'   `censor_source()` objects.
+#'
+#'  *Permitted Values*: `"none"`, `"message"`, `"warning"`, `"error"`
+#'
 #' @details The following steps are performed to create the observations of the
 #'   new parameter:
 #'
@@ -262,10 +271,10 @@
 #'   mutate(STUDYID = "AB42")
 #'
 #' ae <- tribble(
-#'   ~USUBJID, ~AESTDTC,           ~AESEQ, ~AEDECOD,
-#'   "01",     "2021-01-03T10:56", 1,      "Flu",
-#'   "01",     "2021-03-04",       2,      "Cough",
-#'   "01",     "2021",             3,      "Flu"
+#'   ~USUBJID,   ~AESTDTC, ~AESEQ, ~AEDECOD,
+#'   "01",       "2021-01-03T10:56", 1, "Flu",
+#'   "01",       "2021-03-04", 2, "Cough",
+#'   "01",       "2021", 3, "Flu"
 #' ) %>%
 #'   mutate(STUDYID = "AB42")
 #'
@@ -313,6 +322,50 @@
 #'   )
 #' ) %>%
 #'   select(USUBJID, STARTDT, PARAMCD, PARAM, ADT, CNSR, SRCSEQ)
+#'
+#' # Resolve tie when serious AE share a date by sorting with order argument
+#' adsl <- tribble(
+#'   ~USUBJID,    ~TRTSDT,           ~EOSDT,
+#'   "01",        ymd("2020-12-06"), ymd("2021-03-06"),
+#'   "02",        ymd("2021-01-16"), ymd("2021-02-03")
+#' ) %>% mutate(STUDYID = "AB42")
+#'
+#' ae <- tribble(
+#'   ~USUBJID,  ~AESTDTC,      ~AESEQ,  ~AESER,  ~AEDECOD,
+#'   "01",      "2021-01-03",   1,       "Y",    "Flu",
+#'   "01",      "2021-01-03",   2,       "Y",    "Cough",
+#'   "01",      "2021-01-20",   3,       "N",    "Headache",
+#' ) %>% mutate(
+#'   AESTDT = ymd(AESTDTC),
+#'   STUDYID = "AB42"
+#' )
+#'
+#' derive_param_tte(
+#'   dataset_adsl = adsl,
+#'   start_date = TRTSDT,
+#'   source_datasets = list(adsl = adsl, ae = ae),
+#'   event_conditions = list(event_source(
+#'     dataset_name = "ae",
+#'     date = AESTDT,
+#'     set_values_to = exprs(
+#'       EVENTDESC = "Serious AE",
+#'       SRCSEQ = AESEQ
+#'     ),
+#'     filter = AESER == "Y",
+#'     order = exprs(AESEQ)
+#'   )),
+#'   censor_conditions = list(censor_source(
+#'     dataset_name = "adsl",
+#'     date = EOSDT,
+#'     censor = 1,
+#'     set_values_to = exprs(EVENTDESC = "End of Study")
+#'   )),
+#'   set_values_to = exprs(
+#'     PARAMCD = "TTSAE",
+#'     PARAM = "Time to First Serious AE"
+#'   )
+#' )
+#'
 derive_param_tte <- function(dataset = NULL,
                              dataset_adsl,
                              source_datasets,
@@ -322,8 +375,14 @@ derive_param_tte <- function(dataset = NULL,
                              censor_conditions,
                              create_datetime = FALSE,
                              set_values_to,
-                             subject_keys = get_admiral_option("subject_keys")) {
+                             subject_keys = get_admiral_option("subject_keys"),
+                             check_type = "warning") {
   # checking and quoting #
+  check_type <- assert_character_scalar(
+    check_type,
+    values = c("warning", "message", "error", "none"),
+    case_sensitive = FALSE
+  )
   assert_data_frame(dataset, optional = TRUE)
   assert_vars(by_vars, optional = TRUE)
   start_date <- assert_symbol(enexpr(start_date))
@@ -373,8 +432,8 @@ derive_param_tte <- function(dataset = NULL,
       by_vars = by_vars
     )
   }
-
   tmp_event <- get_new_tmp_var(dataset)
+
   # determine events #
   event_data <- filter_date_sources(
     sources = event_conditions,
@@ -382,7 +441,8 @@ derive_param_tte <- function(dataset = NULL,
     by_vars = by_vars,
     create_datetime = create_datetime,
     subject_keys = subject_keys,
-    mode = "first"
+    mode = "first",
+    check_type = check_type
   ) %>%
     mutate(!!tmp_event := 1L)
 
@@ -393,7 +453,8 @@ derive_param_tte <- function(dataset = NULL,
     by_vars = by_vars,
     create_datetime = create_datetime,
     subject_keys = subject_keys,
-    mode = "last"
+    mode = "last",
+    check_type = check_type
   ) %>%
     mutate(!!tmp_event := 0L)
 
@@ -436,7 +497,8 @@ derive_param_tte <- function(dataset = NULL,
     bind_rows(event_data, censor_data),
     by_vars = expr_c(subject_keys, by_vars),
     order = exprs(!!tmp_event),
-    mode = "last"
+    mode = "last",
+    check_type = check_type
   ) %>%
     inner_join(
       adsl,
@@ -505,6 +567,15 @@ derive_param_tte <- function(dataset = NULL,
 #'
 #'   Permitted Values:  `"first"`, `"last"`
 #'
+#' @param check_type Check uniqueness
+#'
+#'   If `"warning"`, `"message"`, or `"error"` is specified, the specified message is issued
+#'   if the observations of the source datasets are not unique with respect to the
+#'   by variables and the date and order specified in the `tte_source()` objects.
+#'
+#'  Default: `"none"`
+#'  Permitted Values: `"none"`, `"warning"`, `"error"`, `"message"`
+#'
 #' @details The following steps are performed to create the output dataset:
 #'
 #'   \enumerate{ \item For each source dataset the observations as specified by
@@ -529,7 +600,7 @@ derive_param_tte <- function(dataset = NULL,
 #' @return A dataset with one observation per subject as described in the
 #'   "Details" section.
 #'
-#' @noRd
+#' @keywords internal
 #'
 #' @examples
 #' library(tibble)
@@ -565,20 +636,22 @@ derive_param_tte <- function(dataset = NULL,
 #'   )
 #' )
 #'
-#' filter_date_sources(
+#' admiral:::filter_date_sources(
 #'   sources = list(ttae),
 #'   source_datasets = list(adsl = adsl, ae = ae),
 #'   by_vars = exprs(AEDECOD),
 #'   create_datetime = FALSE,
 #'   subject_keys = get_admiral_option("subject_keys"),
-#'   mode = "first"
+#'   mode = "first",
+#'   check_type = "none"
 #' )
 filter_date_sources <- function(sources,
                                 source_datasets,
                                 by_vars,
                                 create_datetime = FALSE,
                                 subject_keys,
-                                mode) {
+                                mode,
+                                check_type = "none") {
   assert_list_of(sources, "tte_source")
   assert_list_of(source_datasets, "data.frame")
   assert_logical_scalar(create_datetime)
@@ -613,17 +686,31 @@ filter_date_sources <- function(sources,
       var = !!source_date_var,
       dataset_name = sources[[i]]$dataset_name
     )
-    data[[i]] <- source_dataset %>%
-      filter_if(sources[[i]]$filter) %>%
-      filter_extreme(
-        order = exprs(!!source_date_var),
-        by_vars = expr_c(subject_keys, by_vars),
-        mode = mode,
-        check_type = "none"
-      )
-
+    # wrap filter_extreme in tryCatch to catch duplicate records and create a message
+    data[[i]] <- rlang::try_fetch(
+      {
+        source_dataset %>%
+          filter_if(sources[[i]]$filter) %>%
+          filter_extreme(
+            order = expr_c(exprs(!!source_date_var), sources[[i]]$order),
+            by_vars = expr_c(subject_keys, by_vars),
+            mode = mode,
+            check_type = check_type
+          )
+      },
+      duplicate_records = function(cnd) {
+        cnd_funs <- list(message = cli_inform, warning = cli_warn, error = cli_abort)
+        cnd_funs[[check_type]](
+          paste(
+            "Dataset {.val {sources[[i]]$dataset_name}} contains duplicate records with respect to",
+            "{.var {cnd$by_vars}}"
+          ),
+          class = class(cnd))
+        cnd_muffle(cnd)
+        zap()
+      }
+    )
     # add date variable and accompanying variables
-
     if (create_datetime) {
       date_derv <- exprs(!!date_var := as_datetime(!!source_date_var))
     } else {
@@ -649,7 +736,7 @@ filter_date_sources <- function(sources,
       by_vars = expr_c(subject_keys, by_vars),
       order = exprs(!!date_var),
       mode = mode,
-      check_type = "none"
+      check_type = check_type
     )
 }
 
@@ -782,6 +869,12 @@ extend_source_datasets <- function(source_datasets,
 #'   SRCDOM = "ADSL", SRCVAR = "DTHDT")`. The values must be a symbol, a
 #'   character string, a numeric value, an expression, or `NA`.
 #'
+#' @param order Sort order
+#'
+#'   An optional named list returned by `exprs()` defining additional variables
+#'   that the source dataset is sorted on after `date`.
+#'
+#'   *Permitted Values:* list of variables created by `exprs()` e.g. `exprs(ASEQ)`.
 #'
 #' @keywords source_specifications
 #' @family source_specifications
@@ -793,7 +886,8 @@ tte_source <- function(dataset_name,
                        filter = NULL,
                        date,
                        censor = 0,
-                       set_values_to = NULL) {
+                       set_values_to = NULL,
+                       order = order) {
   out <- list(
     dataset_name = assert_character_scalar(dataset_name),
     filter = assert_filter_cond(enexpr(filter), optional = TRUE),
@@ -803,7 +897,8 @@ tte_source <- function(dataset_name,
       set_values_to,
       named = TRUE,
       optional = TRUE
-    )
+    ),
+    order = order
   )
   class(out) <- c("tte_source", "source", "list")
   out
@@ -844,13 +939,15 @@ tte_source <- function(dataset_name,
 event_source <- function(dataset_name,
                          filter = NULL,
                          date,
-                         set_values_to = NULL) {
+                         set_values_to = NULL,
+                         order = NULL) {
   out <- tte_source(
     dataset_name = assert_character_scalar(dataset_name),
     filter = !!enexpr(filter),
     date = !!assert_expr(enexpr(date)),
     censor = 0,
-    set_values_to = set_values_to
+    set_values_to = set_values_to,
+    order = order
   )
   class(out) <- c("event_source", class(out))
   out
@@ -891,13 +988,15 @@ censor_source <- function(dataset_name,
                           filter = NULL,
                           date,
                           censor = 1,
-                          set_values_to = NULL) {
+                          set_values_to = NULL,
+                          order = NULL) {
   out <- tte_source(
     dataset_name = assert_character_scalar(dataset_name),
     filter = !!enexpr(filter),
     date = !!assert_expr(enexpr(date)),
     censor = assert_integer_scalar(censor, subset = "positive"),
-    set_values_to = set_values_to
+    set_values_to = set_values_to,
+    order = order
   )
   class(out) <- c("censor_source", class(out))
   out
diff --git a/R/filter_extreme.R b/R/filter_extreme.R
index 63bf63838d..7b53645c1f 100644
--- a/R/filter_extreme.R
+++ b/R/filter_extreme.R
@@ -106,7 +106,7 @@ filter_extreme <- function(dataset,
   check_type <-
     assert_character_scalar(
       check_type,
-      values = c("none", "warning", "error"),
+      values = c("none", "warning", "error", "message"),
       case_sensitive = FALSE
     )
   assert_data_frame(dataset, required_vars = by_vars)
diff --git a/inst/WORDLIST b/inst/WORDLIST
index c91f003639..5b8d21b936 100644
--- a/inst/WORDLIST
+++ b/inst/WORDLIST
@@ -312,6 +312,7 @@ msec
 nd
 occds
 onwards
+param
 parttime
 pharmaverse
 pharmaverseadam
diff --git a/man/censor_source.Rd b/man/censor_source.Rd
index 263ac16d6a..ff887ff87d 100644
--- a/man/censor_source.Rd
+++ b/man/censor_source.Rd
@@ -9,7 +9,8 @@ censor_source(
   filter = NULL,
   date,
   censor = 1,
-  set_values_to = NULL
+  set_values_to = NULL,
+  order = NULL
 )
 }
 \arguments{
@@ -36,6 +37,13 @@ censoring.}
 \item{set_values_to}{A named list returned by \code{exprs()} defining the variables
 to be set for the event or censoring, e.g. \code{exprs(EVENTDESC = "DEATH", SRCDOM = "ADSL", SRCVAR = "DTHDT")}. The values must be a symbol, a
 character string, a numeric value, an expression, or \code{NA}.}
+
+\item{order}{Sort order
+
+An optional named list returned by \code{exprs()} defining additional variables
+that the source dataset is sorted on after \code{date}.
+
+\emph{Permitted Values:} list of variables created by \code{exprs()} e.g. \code{exprs(ASEQ)}.}
 }
 \value{
 An object of class \code{censor_source}, inheriting from class \code{tte_source}
diff --git a/man/derive_param_tte.Rd b/man/derive_param_tte.Rd
index 7dadeae6f8..ed312f5244 100644
--- a/man/derive_param_tte.Rd
+++ b/man/derive_param_tte.Rd
@@ -14,7 +14,8 @@ derive_param_tte(
   censor_conditions,
   create_datetime = FALSE,
   set_values_to,
-  subject_keys = get_admiral_option("subject_keys")
+  subject_keys = get_admiral_option("subject_keys"),
+  check_type = "warning"
 )
 }
 \arguments{
@@ -76,6 +77,15 @@ expressions, or \code{NA}.}
 \item{subject_keys}{Variables to uniquely identify a subject
 
 A list of symbols created using \code{exprs()} is expected.}
+
+\item{check_type}{Check uniqueness
+
+If \code{"warning"}, \code{"message"}, or \code{"error"} is specified, the specified message is issued
+if the observations of the source datasets are not unique with respect to the
+by variables and the date and order specified in the \code{event_source()} and
+\code{censor_source()} objects.
+
+\emph{Permitted Values}: \code{"none"}, \code{"message"}, \code{"warning"}, \code{"error"}}
 }
 \value{
 The input dataset with the new parameter added
@@ -278,10 +288,10 @@ adsl <- tribble(
   mutate(STUDYID = "AB42")
 
 ae <- tribble(
-  ~USUBJID, ~AESTDTC,           ~AESEQ, ~AEDECOD,
-  "01",     "2021-01-03T10:56", 1,      "Flu",
-  "01",     "2021-03-04",       2,      "Cough",
-  "01",     "2021",             3,      "Flu"
+  ~USUBJID,   ~AESTDTC, ~AESEQ, ~AEDECOD,
+  "01",       "2021-01-03T10:56", 1, "Flu",
+  "01",       "2021-03-04", 2, "Cough",
+  "01",       "2021", 3, "Flu"
 ) \%>\%
   mutate(STUDYID = "AB42")
 
@@ -329,6 +339,50 @@ derive_param_tte(
   )
 ) \%>\%
   select(USUBJID, STARTDT, PARAMCD, PARAM, ADT, CNSR, SRCSEQ)
+
+# Resolve tie when serious AE share a date by sorting with order argument
+adsl <- tribble(
+  ~USUBJID,    ~TRTSDT,           ~EOSDT,
+  "01",        ymd("2020-12-06"), ymd("2021-03-06"),
+  "02",        ymd("2021-01-16"), ymd("2021-02-03")
+) \%>\% mutate(STUDYID = "AB42")
+
+ae <- tribble(
+  ~USUBJID,  ~AESTDTC,      ~AESEQ,  ~AESER,  ~AEDECOD,
+  "01",      "2021-01-03",   1,       "Y",    "Flu",
+  "01",      "2021-01-03",   2,       "Y",    "Cough",
+  "01",      "2021-01-20",   3,       "N",    "Headache",
+) \%>\% mutate(
+  AESTDT = ymd(AESTDTC),
+  STUDYID = "AB42"
+)
+
+derive_param_tte(
+  dataset_adsl = adsl,
+  start_date = TRTSDT,
+  source_datasets = list(adsl = adsl, ae = ae),
+  event_conditions = list(event_source(
+    dataset_name = "ae",
+    date = AESTDT,
+    set_values_to = exprs(
+      EVENTDESC = "Serious AE",
+      SRCSEQ = AESEQ
+    ),
+    filter = AESER == "Y",
+    order = exprs(AESEQ)
+  )),
+  censor_conditions = list(censor_source(
+    dataset_name = "adsl",
+    date = EOSDT,
+    censor = 1,
+    set_values_to = exprs(EVENTDESC = "End of Study")
+  )),
+  set_values_to = exprs(
+    PARAMCD = "TTSAE",
+    PARAM = "Time to First Serious AE"
+  )
+)
+
 }
 \seealso{
 \code{\link[=event_source]{event_source()}}, \code{\link[=censor_source]{censor_source()}}
diff --git a/man/derive_vars_merged.Rd b/man/derive_vars_merged.Rd
index 700612a4fc..d9d2db5061 100644
--- a/man/derive_vars_merged.Rd
+++ b/man/derive_vars_merged.Rd
@@ -133,7 +133,7 @@ specified for \code{new_vars} can be specified for \code{missing_values}.
 
 \item{check_type}{Check uniqueness?
 
-If \code{"warning"} or \code{"error"} is specified, the specified message is issued
+If \code{"warning"}, \code{"message"}, or \code{"error"} is specified, the specified message is issued
 if the observations of the (restricted) additional dataset are not unique
 with respect to the by variables and the order.
 
@@ -141,7 +141,7 @@ If the \code{order} argument is not specified, the \code{check_type} argument is
 if the observations of the (restricted) additional dataset are not unique with respect
 to the by variables, an error is issued.
 
-\emph{Permitted Values}: \code{"none"}, \code{"warning"}, \code{"error"}}
+\emph{Permitted Values}: \code{"none"}, \code{"message"}, \code{"warning"}, \code{"error"}}
 
 \item{duplicate_msg}{Message of unique check
 
diff --git a/man/derive_vars_merged_lookup.Rd b/man/derive_vars_merged_lookup.Rd
index 6f057576b5..3d2b503dd5 100644
--- a/man/derive_vars_merged_lookup.Rd
+++ b/man/derive_vars_merged_lookup.Rd
@@ -94,7 +94,7 @@ condition.
 
 \item{check_type}{Check uniqueness?
 
-If \code{"warning"} or \code{"error"} is specified, the specified message is issued
+If \code{"warning"}, \code{"message"}, or \code{"error"} is specified, the specified message is issued
 if the observations of the (restricted) additional dataset are not unique
 with respect to the by variables and the order.
 
@@ -102,7 +102,7 @@ If the \code{order} argument is not specified, the \code{check_type} argument is
 if the observations of the (restricted) additional dataset are not unique with respect
 to the by variables, an error is issued.
 
-\emph{Permitted Values}: \code{"none"}, \code{"warning"}, \code{"error"}}
+\emph{Permitted Values}: \code{"none"}, \code{"message"}, \code{"warning"}, \code{"error"}}
 
 \item{duplicate_msg}{Message of unique check
 
diff --git a/man/event_source.Rd b/man/event_source.Rd
index 03e7b4913c..8a721a409e 100644
--- a/man/event_source.Rd
+++ b/man/event_source.Rd
@@ -4,7 +4,13 @@
 \alias{event_source}
 \title{Create an \code{event_source} Object}
 \usage{
-event_source(dataset_name, filter = NULL, date, set_values_to = NULL)
+event_source(
+  dataset_name,
+  filter = NULL,
+  date,
+  set_values_to = NULL,
+  order = NULL
+)
 }
 \arguments{
 \item{dataset_name}{The name of the source dataset
@@ -25,6 +31,13 @@ date from a date character vector to a date object.}
 \item{set_values_to}{A named list returned by \code{exprs()} defining the variables
 to be set for the event or censoring, e.g. \code{exprs(EVENTDESC = "DEATH", SRCDOM = "ADSL", SRCVAR = "DTHDT")}. The values must be a symbol, a
 character string, a numeric value, an expression, or \code{NA}.}
+
+\item{order}{Sort order
+
+An optional named list returned by \code{exprs()} defining additional variables
+that the source dataset is sorted on after \code{date}.
+
+\emph{Permitted Values:} list of variables created by \code{exprs()} e.g. \code{exprs(ASEQ)}.}
 }
 \value{
 An object of class \code{event_source}, inheriting from class \code{tte_source}
diff --git a/man/filter_date_sources.Rd b/man/filter_date_sources.Rd
new file mode 100644
index 0000000000..d411ec9e1e
--- /dev/null
+++ b/man/filter_date_sources.Rd
@@ -0,0 +1,135 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/derive_param_tte.R
+\name{filter_date_sources}
+\alias{filter_date_sources}
+\title{Select the First or Last Date from Several Sources}
+\usage{
+filter_date_sources(
+  sources,
+  source_datasets,
+  by_vars,
+  create_datetime = FALSE,
+  subject_keys,
+  mode,
+  check_type = "none"
+)
+}
+\arguments{
+\item{sources}{Sources
+
+A list of \code{tte_source()} objects is expected.}
+
+\item{source_datasets}{Source datasets
+
+A named list of datasets is expected. The \code{dataset_name} field of
+\code{tte_source()} refers to the dataset provided in the list.}
+
+\item{by_vars}{By variables
+
+If the parameter is specified, for each by group the observations are
+selected separately.
+
+\emph{Permitted Values}: list of variables created by \code{exprs()}
+e.g. \code{exprs(USUBJID, VISIT)}}
+
+\item{create_datetime}{Create datetime variable?
+
+If set to \code{TRUE}, variables \code{ADTM} is created. Otherwise, variables \code{ADT}
+is created.}
+
+\item{subject_keys}{Variables to uniquely identify a subject
+
+A list of symbols created using \code{exprs()} is expected.}
+
+\item{mode}{Selection mode (first or last)
+
+If \code{"first"} is specified, for each subject the first observation with
+respect to the date is included in the output dataset. If \code{"last"} is
+specified, the last observation is included in the output dataset.
+
+Permitted Values:  \code{"first"}, \code{"last"}}
+
+\item{check_type}{Check uniqueness
+
+If \code{"warning"}, \code{"message"}, or \code{"error"} is specified, the specified message is issued
+if the observations of the source datasets are not unique with respect to the
+by variables and the date and order specified in the \code{tte_source()} objects.
+
+Default: \code{"none"}
+Permitted Values: \code{"none"}, \code{"warning"}, \code{"error"}, \code{"message"}}
+}
+\value{
+A dataset with one observation per subject as described in the
+"Details" section.
+}
+\description{
+Select for each subject the first or last observation with respect to a date
+from a list of sources.
+}
+\details{
+The following steps are performed to create the output dataset:
+
+\enumerate{ \item For each source dataset the observations as specified by
+the \code{filter} element are selected. Then for each patient the first or last
+observation (with respect to \code{date}) is selected.
+
+\item The \code{ADT} variable is set to the variable specified by the
+\code{date} element. If the date variable is a datetime variable, only
+the datepart is copied. If the source variable is a character variable, it
+is converted to a date. If the date is incomplete, it is imputed as
+the first possible date.
+
+\item The \code{CNSR} is added and set to the value of the \code{censor}
+element.
+
+\item The selected observations of all source datasets are combined into a
+single dataset.
+
+\item For each patient the first or last observation (with respect to the
+\code{ADT} variable) from the single dataset is selected. }
+}
+\examples{
+library(tibble)
+library(dplyr, warn.conflicts = FALSE)
+library(lubridate)
+
+adsl <- tribble(
+  ~USUBJID, ~TRTSDT,           ~EOSDT,
+  "01",     ymd("2020-12-06"), ymd("2021-03-06"),
+  "02",     ymd("2021-01-16"), ymd("2021-02-03")
+) \%>\%
+  mutate(STUDYID = "AB42")
+
+ae <- tribble(
+  ~USUBJID, ~AESTDTC,     ~AESEQ, ~AEDECOD,
+  "01",     "2021-01-03", 1,      "Flu",
+  "01",     "2021-03-04", 2,      "Cough",
+  "01",     "2021-01-01", 3,      "Flu"
+) \%>\%
+  mutate(
+    STUDYID = "AB42",
+    AESTDT = ymd(AESTDTC)
+  )
+
+ttae <- event_source(
+  dataset_name = "ae",
+  date = AESTDT,
+  set_values_to = exprs(
+    EVNTDESC = "AE",
+    SRCDOM = "AE",
+    SRCVAR = "AESTDTC",
+    SRCSEQ = AESEQ
+  )
+)
+
+admiral:::filter_date_sources(
+  sources = list(ttae),
+  source_datasets = list(adsl = adsl, ae = ae),
+  by_vars = exprs(AEDECOD),
+  create_datetime = FALSE,
+  subject_keys = get_admiral_option("subject_keys"),
+  mode = "first",
+  check_type = "none"
+)
+}
+\keyword{internal}
diff --git a/man/tte_source.Rd b/man/tte_source.Rd
index f63a36d51d..c2c3b56ff7 100644
--- a/man/tte_source.Rd
+++ b/man/tte_source.Rd
@@ -4,7 +4,14 @@
 \alias{tte_source}
 \title{Create a \code{tte_source} Object}
 \usage{
-tte_source(dataset_name, filter = NULL, date, censor = 0, set_values_to = NULL)
+tte_source(
+  dataset_name,
+  filter = NULL,
+  date,
+  censor = 0,
+  set_values_to = NULL,
+  order = order
+)
 }
 \arguments{
 \item{dataset_name}{The name of the source dataset
@@ -30,6 +37,13 @@ censoring.}
 \item{set_values_to}{A named list returned by \code{exprs()} defining the variables
 to be set for the event or censoring, e.g. \code{exprs(EVENTDESC = "DEATH", SRCDOM = "ADSL", SRCVAR = "DTHDT")}. The values must be a symbol, a
 character string, a numeric value, an expression, or \code{NA}.}
+
+\item{order}{Sort order
+
+An optional named list returned by \code{exprs()} defining additional variables
+that the source dataset is sorted on after \code{date}.
+
+\emph{Permitted Values:} list of variables created by \code{exprs()} e.g. \code{exprs(ASEQ)}.}
 }
 \value{
 An object of class \code{tte_source}
diff --git a/tests/testthat/_snaps/derive_param_tte.md b/tests/testthat/_snaps/derive_param_tte.md
index f1438eca6c..21b0a8c31c 100644
--- a/tests/testthat/_snaps/derive_param_tte.md
+++ b/tests/testthat/_snaps/derive_param_tte.md
@@ -61,7 +61,25 @@
       i Following names were provided by `source_datasets`: "adsl"
       i But, `censor_conditions[[1]]$dataset_name = adls`
 
-# list_tte_source_objects Test 14: error is issued if package does not exist
+# derive_param_tte Test 14: detects duplicates in input datasets via pipeline functions
+
+    Code
+      derive_param_tte(dataset_adsl = adsl, start_date = TRTSDT, event_conditions = list(
+        ttae), censor_conditions = list(eot), source_datasets = list(adsl = adsl, ae = ae),
+      set_values_to = exprs(PARAMCD = "TTAE"), check_type = "warning")
+    Condition
+      Warning:
+      Dataset contains duplicate records with respect to `STUDYID`, `USUBJID`, and `AESTDT`
+      i Run `admiral::get_duplicates_dataset()` to access the duplicate records
+    Output
+      # A tibble: 2 x 10
+        USUBJID STUDYID EVENTDESC  SRCDOM SRCVAR  SRCSEQ  CNSR ADT        STARTDT   
+        <chr>   <chr>   <chr>      <chr>  <chr>    <dbl> <int> <date>     <date>    
+      1 01      AB42    AE         AE     AESTDTC      1     0 2021-01-03 2020-12-06
+      2 02      AB42    END OF TRT ADSL   TRTEDT      NA     1 2021-01-30 2021-01-16
+      # i 1 more variable: PARAMCD <chr>
+
+# list_tte_source_objects Test 17: error is issued if package does not exist
 
     Code
       list_tte_source_objects(package = "tte")
diff --git a/tests/testthat/test-derive_param_tte.R b/tests/testthat/test-derive_param_tte.R
index 34067442da..39cf295c5f 100644
--- a/tests/testthat/test-derive_param_tte.R
+++ b/tests/testthat/test-derive_param_tte.R
@@ -932,17 +932,200 @@ test_that("derive_param_tte Test 13: error if dataset_name not in source_datsets
   )
 })
 
+## Test 14: derive_param_tte detects duplicates when check_type = 'warning' ----
+test_that("derive_param_tte Test 14: detects duplicates in input datasets via pipeline functions", {
+  # Define ADSL dataset
+  adsl <- tibble::tribble(
+    ~USUBJID, ~TRTSDT,           ~TRTEDT,           ~EOSDT,
+    "01",     ymd("2020-12-06"), ymd("2021-03-02"), ymd("2021-03-06"),
+    "02",     ymd("2021-01-16"), ymd("2021-01-20"), ymd("2021-02-03")
+  ) %>% mutate(STUDYID = "AB42")
+
+  # Define AE dataset with duplicates
+  ae <- tibble::tribble(
+    ~USUBJID, ~AESTDTC,     ~AESEQ, ~AEDECOD,
+    "01",     "2021-01-03",      1, "Flu",
+    "01",     "2021-03-04",      2, "Cough",
+    "01",     "2021-01-03",      3, "Flu"
+  ) %>% mutate(
+    STUDYID = "AB42",
+    AESTDT = ymd(AESTDTC)
+  )
+
+  # Define event and censor sources
+  ttae <- event_source(
+    dataset_name = "ae",
+    date = AESTDT,
+    set_values_to = exprs(
+      EVENTDESC = "AE",
+      SRCDOM = "AE",
+      SRCVAR = "AESTDTC",
+      SRCSEQ = AESEQ
+    )
+  )
+
+  eot <- censor_source(
+    dataset_name = "adsl",
+    date = pmin(TRTEDT + days(10), EOSDT),
+    censor = 1,
+    set_values_to = exprs(
+      EVENTDESC = "END OF TRT",
+      SRCDOM = "ADSL",
+      SRCVAR = "TRTEDT"
+    )
+  )
+
+  # Run derive_param_tte and check for warning
+  expect_snapshot(
+    derive_param_tte(
+      dataset_adsl = adsl,
+      start_date = TRTSDT,
+      event_conditions = list(ttae),
+      censor_conditions = list(eot),
+      source_datasets = list(adsl = adsl, ae = ae),
+      set_values_to = exprs(PARAMCD = "TTAE"),
+      check_type = "warning"
+    )
+  )
+})
+
+## Test 15: derive_param_tte resolves ties using order argument when input is sorted descending
+test_that("derive_param_tte Test 15: derive_param_tte resolves ties using order argument when
+input is sorted descending", {
+  adsl <- tibble::tribble(
+    ~USUBJID, ~TRTSDT,           ~EOSDT,
+    "01",     ymd("2020-12-06"), ymd("2021-03-06"),
+    "02",     ymd("2021-01-16"), ymd("2021-02-03")
+  ) %>%
+    mutate(STUDYID = "AB42")
+
+  # Sort the input AE dataset in descending order by AESEQ
+  # to confirm that the order argument re-sorts it correctly.
+  ae <- tibble::tribble(
+    ~USUBJID, ~AESTDTC,     ~AESEQ, ~AESER, ~AEDECOD,
+    "01",     "2021-01-03",  2,     "Y",    "Cough",
+    "01",     "2021-01-03",  1,     "Y",    "Flu",
+    "01",     "2021-01-20",  3,     "N",    "Headache"
+  ) %>%
+    mutate(
+      STUDYID = "AB42",
+      AESTDT = ymd(AESTDTC)
+    ) %>%
+    arrange(desc(AESEQ)) # Intentionally sort descending to test the order argument
+
+  result <- derive_param_tte(
+    dataset_adsl = adsl,
+    start_date = TRTSDT,
+    event_conditions = list(event_source(
+      dataset_name = "ae",
+      date = AESTDT,
+      set_values_to = exprs(
+        EVENTDESC = "Serious AE",
+        SRCSEQ = AESEQ
+      ),
+      filter = AESER == "Y",
+      order = exprs(AESEQ) # Should re-sort so that AESEQ=1 (Flu) is chosen on tie
+    )),
+    censor_conditions = list(censor_source(
+      dataset_name = "adsl",
+      date = EOSDT,
+      censor = 1,
+      set_values_to = exprs(EVENTDESC = "End of Study")
+    )),
+    set_values_to = exprs(
+      PARAMCD = "TTSAE",
+      PARAM = "Time to First Serious AE"
+    ),
+    source_datasets = list(adsl = adsl, ae = ae)
+  )
+
+  # Check that for USUBJID = "01", the first serious AE selected is the one with AESEQ = 1 (Flu),
+  # despite the input AE data initially being arranged to show AESEQ=2 (Cough) first.
+  selected_seq <- result %>%
+    filter(USUBJID == "01", PARAMCD == "TTSAE") %>%
+    pull(SRCSEQ)
+
+  expect_equal(selected_seq, 1, info = "The order argument should ensure AE with AESEQ=1
+  is chosen on tie.")
+})
+
+## Test 16: derive_param_tte produces consistent results regardless of input sort order ----
+test_that("derive_param_tte Test 16: produces consistent results regardless of input sort order", {
+  # Define ADSL dataset
+  adsl <- tibble::tribble(
+    ~USUBJID, ~TRTSDT,           ~TRTEDT,           ~EOSDT,
+    "01",     ymd("2020-12-06"), ymd("2021-03-02"), ymd("2021-03-06"),
+    "02",     ymd("2021-01-16"), ymd("2021-01-20"), ymd("2021-02-03")
+  ) %>% mutate(STUDYID = "AB42")
+
+  # Define AE dataset with duplicates
+  ae <- tibble::tribble(
+    ~USUBJID, ~AESTDTC,     ~AESEQ,  ~AEDECOD,
+    "01",     "2021-01-03",      1,  "Flu",
+    "01",     "2021-03-04",      2,  "Cough",
+    "01",     "2021-01-03",      3,  "Flu"
+  ) %>% mutate(STUDYID = "AB42", AESTDT = ymd(AESTDTC))
+
+   # Define event and censor sources
+  ttae <- event_source(
+    dataset_name = "ae",
+    date = AESTDT,
+    order = exprs(AESTDT, AESEQ),
+    set_values_to = exprs(
+      EVENTDESC = "AE",
+      SRCDOM = "AE",
+      SRCVAR = "AESTDTC",
+      SRCSEQ = AESEQ # Ensure AESEQ is included here
+    )
+  )
+
+  eot <- censor_source(
+    dataset_name = "adsl",
+    date = pmin(TRTEDT + days(10), EOSDT),
+    censor = 1,
+    set_values_to = exprs(
+      EVENTDESC = "END OF TRT",
+      SRCDOM = "ADSL",
+      SRCVAR = "TRTEDT"
+    )
+  )
+
+  # Run derive_param_tte with sorted AE dataset
+  result_sorted <- derive_param_tte(
+    dataset_adsl = adsl,
+    start_date = TRTSDT,
+    event_conditions = list(ttae),
+    censor_conditions = list(eot),
+    source_datasets = list(adsl = adsl, ae = arrange(ae, AESEQ)),
+    set_values_to = exprs(PARAMCD = "TTAE"),
+    check_type = "warning"
+  )
+
+  # Run derive_param_tte with reverse-sorted AE dataset
+  result_unsorted <- derive_param_tte(
+    dataset_adsl = adsl,
+    start_date = TRTSDT,
+    event_conditions = list(ttae),
+    censor_conditions = list(eot),
+    source_datasets = list(adsl = adsl, ae = arrange(ae, desc(AESEQ))),
+    set_values_to = exprs(PARAMCD = "TTAE"),
+    check_type = "warning"
+  )
+
+  expect_equal(result_sorted, result_unsorted)
+})
+
 # list_tte_source_objects ----
-## Test 14: error is issued if package does not exist ----
-test_that("list_tte_source_objects Test 14: error is issued if package does not exist", {
+## Test 17: error is issued if package does not exist ----
+test_that("list_tte_source_objects Test 17: error is issued if package does not exist", {
   expect_snapshot(
     list_tte_source_objects(package = "tte"),
     error = TRUE
   )
 })
 
-## Test 15: expected objects produced ----
-test_that("list_tte_source_objects Test 15: expected objects produced", {
+## Test 18: expected objects produced ----
+test_that("list_tte_source_objects Test 18: expected objects produced", {
   expected_output <- tibble::tribble(
     ~object,            ~dataset_name,                                              ~filter,
     "ae_ser_event",            "adae",                 quote(TRTEMFL == "Y" & AESER == "Y"),
diff --git a/tests/testthat/test-user_utils.R b/tests/testthat/test-user_utils.R
index 317363665e..20ff1e624d 100644
--- a/tests/testthat/test-user_utils.R
+++ b/tests/testthat/test-user_utils.R
@@ -165,7 +165,8 @@ test_that("print.source Test 13: `source` objects are printed as intended", {
     "  EVENTDESC: \"AE\"",
     "  SRCDOM: \"AE\"",
     "  SRCVAR: \"AESTDTC\"",
-    "  SRCSEQ: AESEQ"
+    "  SRCSEQ: AESEQ",
+    "order: NULL"
   )
   expect_identical(capture.output(print(ttae)), expected_print_output)
 })