this would be used for cases where a song wasn't written or arranged for the target work (i.e. soundtrack, musical, opera, etc.), but was included pretty much as-is, such as the Pulp Fiction or Baby Driver soundtracks (which are largely popular songs), jukebox musicals, and tracks from one game being used in a later game (but not a new arrangement)

to that end, might make sense to make it a subtype of the "part of" relationship