Thanks for the reply. I guess I haven't had that happen to me yet with videos I'm looking for again having gone private.
I'm also not interested in crappy, privacy-invading, ad-shoving YouTube apps, which is why I mentioned SmartTube. In case you haven't heard of it, it's FOSS and has AdBlock & SponsorBlock integrated. It's designed for TV use. If Tube Archivist fits your need though, that's great.