Speculative fraud hypothesis

[dexdex]

Big manuscripts, especially illustrated ones, were expensive. It would be entirely understandable that someone who could not afford them would create one to raise his/her status as a practitioner of some more or less secret art (alchemy, herbalism, astrology). More or less because, of course, there were books in circulation, but each practitioner had their own recipes and kept the good stuff private.

You say I can't have my own book of secrets? Hold my beer. The whole family participated (some of them had terrible handwriting) and the little nephew (age 8-10) did the coloring.

Precisely. Maybe not that extreme with the nephew   - the scribe(s) had to have access to a pretty legit library and know how to scribe, as well as have the means to get the supplies. But a quack with a few of his unscrupulous student friends at some monasterial school? Why not?