Now, I am having trouble believing that.
MJ used to record his vocals even for songs that he was rather unsure, or not totally happy with, or even for songs that he was just experimenting on them, especially until the direction of the album was beginning to crystallize.
After that point, many of those songs (with his vocals on them) that did not fit to the album’s direction/flow had to remain unreleased.
Rodney Jerkins has already explained it when he was asked about MJ’s unreleased material.
“... I really want people to hear some of the stuff we did together which never made the cut… There’s a whole lot of stuff, just as good, maybe better. People have gotta hear it… Michael records hundreds of songs for an album, so we cut it down to thirty-five of the best tracks, and picked from there. It’s not always about picking the hottest tracks, it’s gotta have a flow, so there’s a good album’s worth of material that could blow your mind …” (Rodney Jerkins, Cut Magazine)
Rodney Jerkins clearly refers not only to many songs (with MJ’s vocals on them) that did not make the ‘Invincible’ album, but also for many other songs (with MJ’s vocals on them, again) that did not make his previous studio albums.