Watching that other discussion. Maybe a better hint towards “artist intent” is needed.
It was easy when it was physical due to the cost of making the media. People didn’t usually give things away without reason.
Now music has no physical replication cost it is much easier for an artist to literally give away their official music if they so choose to. Whereas other times they are making it clear this is a promotion.
It is a tough and confusing line as a lot of music is released to promote interest. Singles promote interest in an album. But in MB language “promotional” has a tighter definition that is also saying “this is not part of an official catalogue”