So, to explain in more detail: I read about a new community on newcommunities and I decided to search for it so that it started federating with Kbin.
However, when I visit the community on lemmy.world, there are already 32 posts from before the community became visible on kbin, but I can only see the posts that were made after I “discovered” the community on Kbin.
I just tested it with my account on lemmy.world, and the posts do indeed show up on Kbin now.
That’s really good to know. Thank you so much for the explanation!