Aside from the fact that many albums never made it into the digital age, the jump from vinyl to CDs as the music industry's main format also meant truncated versions of certain records as well.
Case in point: Side 4 of Genesis' self-explanatory Three Sides Live [Atlantic-1982] includes 5 studio tracks, two of which, "Paperlate" and "You Might Recall", were dual A-sides on the UK EP 3 x 3 [Charisma-1982]. The former became a hit single, but "You Might Recall" only got minor exposure and was more or less banished to obscurity when Three Sides Live was released on CD with the studio tracks excised. However, "You Might Recall"--which was originally slated for Abacab [Atlantic-1981] and is now available on the Genesis 1976-1982 [Atlantic-2007] or Genesis 1976-1992 [Atlantic-2000] box sets--is the more interesting of the two and is practically--at this point anyway--a long, lost Genesis single. It's also proof that Phil Collins' pop leanings within the band weren't always a bad thing.