Keep track of episodes added to library even if no longer in feed

[rwfuller]

There are a few podcast feeds which limit the number of entries in the feed even though the older podcasts no longer in the feed will still download. Here are a couple of feeds which do this.

The Ticket Top 10 (limit 100) (10 / daily)
https://www.omnycontent.com/d/playlist/a7b0bd27-d748-4fbe-ab3b-a6fa0049bcf6/685ad9ad-9963-4aab-a428-a88d0111928c/1784923a-360f-49ea-b992-a88d01119295/podcast.rss

This American Life (limit 10) (1 / weekly)
https://www.thisamericanlife.org/podcast/rss.xml

The expectation would be the application would keep track of older episodes which have been added to library even if they are no longer in the feed.