The 16 remaining songs thing has always bothered me. I mean for one the Estate need permission to use some of the songs (Will I Am, Redone, Quincy tracks) so they couldn't have been up for consideration.
Next you have the LA Reid comments, him only being interested in songs "Michael sung top to bottom" which Mike clearly didn't for the first single LNFSG (clearly it was a good soundbite and nothing more)
Then you have Bryan Loren saying the Estate wasn't interested in his songs at all.
So just on that alone I believe there must be more than 16 tracks left, rather they chose from 24 tracks that LA Reid liked and narrowed down for the 8 tracks for Xscape.
If I were a betting man, I'd assume they've located more songs in that 10 years since Xscape as well