Writing a post, scheduling it, and publishing it to connected accounts.
One post, several destinations
A post you write can go to several accounts at once. Each destination publishes separately and can fail separately.
That is why a post has a partial state: some destinations published and some did not. It is neither a success nor a failure, and it is exactly what happened.
Publishing happens in the background
A scheduled post is published by a background worker. The time you set means "not before this", not that exact second.
Two pages, two jobs
Accounts is where connections are made and checked. Calendar is where posts are written, scheduled, and their outcome seen.