This has been brought up a few times, but I don’t know if it’s ever been formally discussed.
If you pore through most any rights society database, you might find alternate versions of a work listed with separate identifiers from the original. Sometimes there are even differing credits (writers, publishers or both). Traditional MB wisdom dictates that remixes and most* alternate versions use the same works as the original, but this is too big an edge case to ignore. Theoretically we could add the alternate versions’ identifiers to the core work, but the only way to identify the source of said identifiers is via an annotation.
*Traditionally, the only exception to this is if the lyrics are modified.