Enlarged diagram on f68v2-f68v1?

[Jorge_Stolfi]

Objectively, it should have been very valuable to some scholars

If this is indeed the case, then it was more likely that the book was [not] sold. ... It seems unlikely to me that a person who has worked hard on a manuscript would agree to sell it himself, but who knows...

On the contrary: the transposition to vellum, with lots of blank spaces and apparently meaningless decoration, only makes sense if the vellum copy was meant for someone else.  None of that would be needed if the Author himself was the only intended reader: for that, his draft on paper would have  been enough.

Maybe he did not intend to sell, but to give as a present to a good scholar friend.  Or to a local big shot, in the hope of receiving some benefit in return.  Or maybe he meant to leave it as legacy to his heirs, or to the world.  

But "for sale" seems at least as likely as those alternatives.   Especially considering the quality of the vellum and the, let's say, limited skills of the Scribe that he recruited: he probably was rather strained financially when he decided to create the vellum copy.

[It is more likely that the book was] sold not by the author, but by the second owner who made the notes on f17r, f66v, and f116v, as he received the manuscript directly from the author.

I don't see any reason to assume that the author of the marginalia had contact with the Author.  On the contrary, I suspect that the marginalia were added by someone who did not understand the book at all.

All the best, --stolfi