One more thing that makes it a bit more confusing for me is that there are eight Greatest Hits groups for Nazareth on Discogs. With artwork and basic info they are:
12 tracks. 102 versions.
18 tracks. 4 versions.
17 tracks. 1 version.
11 + 7 tracks. 1 version.
12 tracks. 1 version (cassette).
12 tracks. 1 version (vinyl).
15 tracks. 1 version (CD reissue).
12 tracks. 1 version (CD).
Of these, three (1, 5 and 6) have the same (12-track) track list, and could be considered part of the same release group, even though some of the artwork differs. Further, the 15-track number 7 has the same first 12 tracks (although in a slightly different order – track 1 is moved to the track 6 position), and could possibly be considered part of the same group (with 3 bonus tracks).
The others have significantly different track lists such that that they could probably justify being different release groups.
After reviewing this, I’ve initiated Edit 47241614 to move the 12-track release into the same release group with the 15-track release.