As he has his own studio, I imagine there's an awful lot of stuff that has never been booted, and probably will never see the light of day. I expect that Macca takes all his master tapes home with him and locks them up. There seem to be very few outtakes and alternate versions on Paul's bootlegs as far as I can see. And as far as I know, there are no Band On The Run outtakes. An Anthology would be very interesting.