As @mfmeulenbelt says, the way scan works is that it has to find a matching AcoustID in the database to pull from.
If it finds more than one AcoustID, that's when the slider settings will take effect to decide which one to use.
There's a few reasons why this might not be happening for you:
- Someone has submitted the AcoustID for the compilation but not the release (the recordings can probably be merged in these cases, if we know they're the same)
- The album release doesn't exist (yet)
- You don't have the album version of a track, in which case the AcoustID (correctly) only matches a VA compilation or other release that had your version on it
You can check any of these yourself - if you look at a recording on the MusicBrainz website, you can look at the fingerprints tab to see what's in there. We can't really help more without some specific examples or albums/ acoustID's etc!
As a side note, please don't hit 'submit' (submitting your scanned AcoustID's) unless you're 100% sure you're submitting a track from the right release to the right release, including different versions etc, in MB.