If single song has an artist and title in metadata then we do a search for that and if we get results that is what we use (plus acoustid). However if popular artist they may have many different versions of song and because max of 20 results some candidate releases will not be returned because otherwise would take too long to match, so may be left with the wrong (va releases). What we should do is search by artist title and release and only if get no/few matches do search by just artist and title.
Addtionally we could allow search return more results then we want then filter them out.
Additionally perhaps we should score more releases (but this will slow things down)