That's what's been said for many many years... but I have never been able to hear a paper sheet. And, in the last year or so, a different vocal cut has been release like a demo, so I'm guessing it is not true with the album version of the song.
Maybe, MAYBE, it is a situation like Into the groove, in which the "don't touch this demo this song is perfect" situation is in the movie, but when it comes to comercial release, they re-recorded the vocals?