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It means both instances will see old posts from before one of them defederated.
Now that A is de-federated from B, they both won’t see new posts or comments from eachother. In the case of fedia and ani.social, you won’t get any new posts from any of their communities or users. If you post on [email protected] from fedia, nobody will see that post outside of fedia users, because ani.social isn’t seeing it and passing it around to the rest of the fediverse.
You hav basically the right idea, everything stops syncing when one defederates.
Uhhuh. “Feedback”, read: risk of class action lawsuits from everybody they tried stopping from reaching the support they paid for