The post that went to the wrong account
A publication identifier is an optional field that silently defaults. The API reports success either way, so the only way to know is to verify the response.
syndication
4 posts
One of the two links is always missing
A syndicated copy links home immediately; the original links out only after a rebuild. The asymmetry means one direction is reliably broken for a while.
Syndicate to a 404 and you donate the SEO
A canonical that 404s when the syndicating platform fetches it does not transfer authority. Their copy becomes the original, and the order is the whole fix.
A tag feed is not a list of your posts
A feed returns what it decided to include, not everything that exists. Reading a lower bound as a complete list produces duplicates and false gaps.