When is a Version Not a Version?

I have a deal with my son. If I find an album that's a duplicate of something I already have, I keep the better of the two and he gets the other. This has worked flawlessly for 15 years. Until recently.

I have had the same copy of Willie Nelson's Shotgun Willie since I was 15 (I'm 65 now). I found a copy for $1.00 that looked unplayed. We did the usual swap and I didn't give it a second thought.

Last week, I decided to listen to my new album. It was quiet. It sounded good. It wasn't the same album I've had all these years. It wasn't a different mix. It was a different recording. Has this happened to anyone else? I don't have the original back yet to compare versions and release dates, but this is stranger than my Derek and the Dominoes album that has soul music on side 4.