When single song matching against Acoustid ensure we are selecting the correct song, the way we use Acoutid we are returning releases that containing a track with the said id and then checking the song against the songs on the release, but we don't prevent the song matching a different song to the release which may seem to be a better match even if not matching Acoustid. For single song matching we are only trying to score one song on the release so we need to tighten this up to prevent invalid matching.
We do already make a list of any songs matched to a song on release with different acoustid and then not allow if the title of the track we have matched to isnt a reaonable match to the track title of the acoustid of the track on the release.
1.only checks title not artist.
2.We only do this if recording we have matched to has an acoustid, if it does not we dont do further checking we just assume okay.
The correct way to do this is to not to just pass a set of releases to score against, but change datastructure so that you know which releases were found by metadata match and which were found by acoustid and take account of this when just matching single track to release.