I don't think you should say in the documentation that "if a track is the only or definitive version of a song, no song topic is needed". Every track should point to one or more songs, because there are certain attributes (composer, lyricist) that belong to the song, not the track.
(Note the "one or more songs" above. A track like Springsteen's "Devil with the blue dress / Good golly Miss Molly / Jenny Jenny" should be a single track pointing to three songs.

