diff --git a/activitysim/core/workflow/checkpoint.py b/activitysim/core/workflow/checkpoint.py
index b553460a2..b7fe5900a 100644
--- a/activitysim/core/workflow/checkpoint.py
+++ b/activitysim/core/workflow/checkpoint.py
@@ -958,7 +958,9 @@ def restore_from(self, location: Path, checkpoint_name: str = LAST_CHECKPOINT):
         self.load(checkpoint_name, store=from_store)
         logger.debug(f"checkpoint.restore_from of {checkpoint_name} complete")
 
-    def check_against(self, location: Path, checkpoint_name: str):
+    def check_against(
+        self, location: Path, checkpoint_name: str, strict_categoricals: bool = False
+    ):
         """
         Check that the tables in this State match those in an archived pipeline.
 
@@ -966,6 +968,11 @@ def check_against(self, location: Path, checkpoint_name: str):
         ----------
         location : Path-like
         checkpoint_name : str
+        strict_categoricals : bool, default False
+            If True, check that categorical columns have the same categories
+            in both the current state and the checkpoint.  Otherwise, the dtypes
+            of categorical columns are ignored, and only the values themselves are
+            checked to confirm they match.
 
         Raises
         ------
@@ -1033,9 +1040,27 @@ def check_against(self, location: Path, checkpoint_name: str):
                         local_table[ref_table.columns], ref_table, check_dtype=False
                     )
                 except Exception as err:
-                    raise AssertionError(
-                        f"checkpoint {checkpoint_name!r} table {table_name!r}, {str(err)}"
-                    )
+                    if not strict_categoricals:
+                        try:
+                            pd.testing.assert_frame_equal(
+                                local_table[ref_table.columns],
+                                ref_table,
+                                check_dtype=False,
+                                check_categorical=False,
+                            )
+                        except Exception as err2:
+                            raise AssertionError(
+                                f"checkpoint {checkpoint_name!r} table {table_name!r}, {str(err)}\nfrom: {str(err2)}"
+                            )
+                        else:
+                            warnings.warn(
+                                f"checkpoint {checkpoint_name!r} table {table_name!r}, "
+                                f"values match but categorical dtype does not"
+                            )
+                    else:
+                        raise AssertionError(
+                            f"checkpoint {checkpoint_name!r} table {table_name!r}, {str(err)}"
+                        )
                 else:
                     logger.info(f"table {table_name!r}: ok")
 
diff --git a/activitysim/core/workflow/state.py b/activitysim/core/workflow/state.py
index 479b032c7..e00e20c94 100644
--- a/activitysim/core/workflow/state.py
+++ b/activitysim/core/workflow/state.py
@@ -1082,16 +1082,23 @@ def extend_table(self, table_name, df, axis=0):
                 missing_df_str_columns = []
 
             # union categoricals
-            for c in table_df.columns.intersection(df.columns):
-                if isinstance(table_df[c].dtype, pd.api.types.CategoricalDtype):
-                    if isinstance(df[c].dtype, pd.api.types.CategoricalDtype):
-                        from pandas.api.types import union_categoricals
-
-                        uc = union_categoricals([table_df[c], df[c]])
-                        table_df[c] = pd.Categorical(
-                            table_df[c], categories=uc.categories
-                        )
-                        df[c] = pd.Categorical(df[c], categories=uc.categories)
+            for c in table_df.columns:
+                if c in df.columns:
+                    if isinstance(table_df[c].dtype, pd.api.types.CategoricalDtype):
+                        if isinstance(df[c].dtype, pd.api.types.CategoricalDtype):
+                            from pandas.api.types import union_categoricals
+
+                            uc = union_categoricals([table_df[c], df[c]])
+                            table_df[c] = pd.Categorical(
+                                table_df[c], categories=uc.categories
+                            )
+                            df[c] = pd.Categorical(df[c], categories=uc.categories)
+                else:
+                    # when the existing categorical type has an empty string as a category,
+                    # we will use that as the missing value instead of NaN
+                    if isinstance(table_df[c].dtype, pd.api.types.CategoricalDtype):
+                        if "" in table_df[c].cat.categories:
+                            missing_df_str_columns.append(c)
 
             # preserve existing column order
             df = pd.concat([table_df, df], sort=False, axis=axis)
diff --git a/activitysim/examples/external_example_manifest.yaml b/activitysim/examples/external_example_manifest.yaml
index 0be270636..5face8e8e 100644
--- a/activitysim/examples/external_example_manifest.yaml
+++ b/activitysim/examples/external_example_manifest.yaml
@@ -13,11 +13,11 @@
 #
 
 prototype_mtc:
-  url: https://github.com/jpn--/activitysim-prototype-mtc/archive/refs/tags/v1.3.1.tar.gz
+  url: https://github.com/ActivitySim/activitysim-prototype-mtc/archive/refs/tags/v1.3.1.tar.gz
   sha256: ec53c6e72da1444bd5808de8c644cea75db284dfcc419b776575ba532b3ccb87
   assets:
     test/prototype_mtc_reference_pipeline.zip:
-      url: https://github.com/jpn--/activitysim-prototype-mtc/releases/download/v1.3.1/prototype_mtc_reference_pipeline.zip
+      url: https://github.com/ActivitySim/activitysim-prototype-mtc/releases/download/v1.3.1/prototype_mtc_reference_pipeline.zip
       sha256: 394e5b403d4c61d5214493cefe161432db840ba4967c23c999d914178d43a1f0
 
 estimation_example: