Crucially, the posts did not exist even if I visited the profile page of the account: even after weeks of daily posts, the profile page displayed by mastodon.social claimed the account had never posted, and the posts would only begin appearing after someone on mastodon.social began following the account.

I hate this. Even assuming that my server can't host every message ever posted on the network, why can't it go and talk to the other server and fetch a timeline so that I don't see a completely empty account for a user that didn't happen to have their messages relayed to my server?

Same when opening threads.