Speculative fraud hypothesis

[ReneZ]

I believe there's a misunderstanding here: people's motivations haven't changed, and it would be a plausible reason to do this if you stood to gain what the sale to Rudolf did.

Let us distinguish between motivations of buyers, motivations of sellers and motivations of fakers.

All of these will have changed over the centuries.

There are undoubtedly publications about the book market that are relevant for this topic, but I know from 'personal communication' that there was not much of an 'old book market' more than 150 years ago.
Books were dealt (often appropriated) in collections by rulers and by libraries. Think of Napoleon as the most obvious example.

It is only in the presence of such a market that creating and selling fakes for profit may become interesting.
 
The conditions have changed dramatically, also between the early 15th century and Rudolf's times.