Yes- if anyone interacts with those posts after the community has been federated then the entire post gets sent over. eg: someone "likes" a comment or posts a new comment.

@ChrisFhey I was playing around with accounts on multiple lemmy/kbin instances and making communities to see what would happen. I made communities which wouldn't be very attractive to others and didn't promote them at all to see how it would go if left alone.

From what I can tell:

• Say you create a community on kbin.social July 1
• Each day at 00:01am, you make 1 post.
• On July 5, an account on lemmy.world subscribes to the community
• lemmy.world can see posts made July 6 onwards
• if lemmy.world account goes to the kbin.social URL (on community home instance) for the July 3 post , copies the URL to fediverse, searches the URL on lemmy.world, that post will now be available on lemmy.world

So to get a new community going across instances, especially a niche one, a bit of working the system might be needed. The best thing would be to make one account on the top x instances, then use each account to search for each existing post.

This would be a "bot" thing arguably but it would one require 1 account to do 1 search per post to create the "interaction". I am not sure if each comment requires the same treatment as I haven't delved into that. This is pretty slow to do. There was a lot of waiting to see if stuff would happen on its own. Which mostly it doesn't.

If anyone thinks I'm wrong about the details, please tell me. This is just what I thinking goes on.

No.

yes this happens, but it resolves itself over time, and the posts will show up within a few hours or days. this happened to me on a few of my mags i federated between kbin/lemmy, eventually all the posts showed up 👍🏼