The Modern Forgery Hypothesis

[asteckley]

But why use XVth century imagery if his aim was to pass it as a lost work of Bacon? That would be quite weird to do, given his expertise with rare books. Why not use XIIIth century imagery?

Well, that would depend on when he nailed down the specifics of his aim, wouldn’t it.
The story considers "even though not consciously aiming to restrict his content to a specific historical period".