I checked some other things, a few hours ago, but then had an unpleasant distraction.

Before I forget completely: whilst the tagged BSD Cafe Billboard post did appear in the corresponding tagged area of beige.party Mastdon, the post does not appear as a post (or reply) from me in BSD Cafe Mastodon. That makes sense, I guess; no real need for a federated post to be in two separate services within the same domain. Or is there a need?

(At the foot of the Billboard post I addressed two Mastodon IDs, wondering whether there would be a share effect.)