This release adds a new command, elfeed-tube-fill-feeds:
Youtube RSS feeds only contain the last 15 videos from a channel. So you will only collect entries for videos from a little before when you subscribe to a channel's feed.
Elfeed Tube now provides a command to add all historical entries for Youtube feeds to Elfeed. Call elfeed-tube-fill-feeds in an Elfeed search or entry buffer to fetch all historical entries for the feed at point. You can do this for many feeds at once by selecting a region of entries.