This is one of those double edged sword things with Lemmy, since there’s so many places a community can be, they all end up being a little smaller. There’s got to be a better solution for that. Maybe when creating a community there should be a way to automatically search a large portion of committed all at once and display it to the user.
I’ve found that sometimes old posts don’t propagate to newer servers. So if you want to participate in a old thread, you need another account.