the later tracks comprise the 3rd disc of the original Deluxe CD set, with notable tracks, singles, duets etc from throughout his career, i don't know for sure but i don't think sales were a determining factor in their inclusion.I'd ask. On this Diamonds release, are the songs based on the number of album sales? On some of these later songs I'm very unfamiliar with some of those tracks.
I would have loved if some of his earlier songs were included here.
Captain Fantastic and the Brown Dirt Cowboy
Madman Across the Water
Funeral For A Friend/Love Lies Bleading
Tower of Babel
.... many others
fans were clamouring for a hits compilation that included tracks beyond the established "Jukebox" of Hits (as Elton himself calls the 70's & 80's Standards) so when Diamonds first came out certain tracks were very welcome additions including "Island Girl", "Song For Guy", "The One", The Lion King, etc.