I've been wondering about this too. Most of the tracks have a very well rounded and full sound to them. On the other hand, the loudness levels are all over the place from track to track.
Yeah, I agree... volume is all over the place. As a whole, I don't think they've been mastered... yet.
But some tracks do sound full & beefy. (Dark Girl/Boy for example) ... so maybe some of them in the past
where grouped for bonus or ep track mastering, but never used.