I already have a good picture of the use of human skin as book-cover material in France and Europe from 1500 to 1900, i.e., not that rare.
But apparently to do that, human skin, like other forms of fine leather had to be reinforced or mounted on stiffer backing, because of its thinness and flexibility.
Thus the material itself is obviously better suited to the inner pages of codices (handmade books prior to printing), and I am suspicious that it may have been used in place of animal skins for both parchment/vellum books and also scrolls.
The idea of using human skin for various purposes is obviously very old, and so I think there must be some evidence of its use as book-page material somewhere in the pre-printing era.
thanks in advance,