The definitive version in any context means the version that defines the song; the benchmark by which all else is judged; Of recognized authority or excellence, perhaps. Authoritative, classical, determinate, unequivocal. Then of course we could have, conclusive, explicit, expressed, standard.

Or to be more obtuse "Pick the bones out of that one!"

Incidentally, have you listened to Paul's version on 'Your welcome here kind stranger'? You'll know what is meant then.*BG*

B.