I want to limit this to analog recordings because you typically don't have this problem with something that was recorded digitally and included it's debut on CD.
Mastering changes a lot of what was actually mixed down in the studio. I've encountered this particular phenomenon many times, but I just got two versions of an album on CD (Comus' First Utterance) where one of them has the very first track being one of the loudest (+1 dB over the average) and the last track being one of the quietest (-3 dB under the average), but on the other CD it's the opposite. The first track is very quiet and the last one is loud.
Usually these volume differences are small enough to not really matter, but on a factor of 3 dB this is quite audible and it changes the experience a bit. Do you start the album on a loud note and end softly? Or vice versa? Which was intended by the artists? There's really no way to tell. I don't know which CD is more true to the tapes they were taken from.
One might say that the vinyl is the "definitive" listen - it's how it was first heard by the world. Equalization speaking, I wouldn't completely agree, because what was mixed down in the studio has to be equalized to make sure it tracks right on vinyl. But relative per-song volume I can agree more often. Yet when I heard the first UK press LP of King Crimson's Red I was very disappointed to hear that the title song, the first one on the LP, was very quiet compared to the rest of the album. It's a hard song too, so it really loses its edge if you adjust your volume according to the rest of the album. The other option is to adjust it to that song and let the remainder of the album bash your ears. Is that what KC had intended? Or is that a creative decision of the mastering engineer? No digital version of the album has the first track so quiet... (relatively speaking)
It's frustrating.








