The Modern Forgery Hypothesis

[ReneZ]

Hm, here I don't follow.  If we assume that Wilfrid was morally capable of forgery or other fraud, the mere fact that access to the Carteggio was restricted by the Jesuits does not mean that he did not get to peruse it.  Priests are not saints...

There is a lot of documented evidence that makes it clear that nobody 'outside' knew what was hidden inside the Villa Torlonia. This evidence is not generally known, and to be able to argue about it means reading up on a lot. Note that the carteggio is just 14 out of (at least) 2000 volumes that they were hiding there. 

To copy the handwriting of the Carteggio letter written by Marci's scribe (even as we agree that this would be an almost superhuman feat) would have required looking directly at this letter for a longer time.

The official bibliographer of the Society of Jesus, who was tasked by Petrus Beckx himself to update and extend the voluminous catalogue of all Jesuit writings, DID NOT KNOW that the Carteggio of Kircher existed in the Villa Torlonia. Or if he had this information, he was clearly forbidden to add it to this catalogue. 

The threat of continued confiscation was very real. The few hundred 'plain old' classics like Ceasar and Cicero were perhaps the least of their worries, but the writings of their founders and famous historical Jesuits needed to be protected. 
The Jesuits could have made a lot more money by selling more of their classics to Voynich, but they considered it was too dangerous. The Vatican paid a lot less, but it was safer. After that, the Vatican were themselves worried that the state might find out that they bought these books which the state considered their property.

The Jesuits were at risk to lose a lot.

In 1896, while all this material was hidden in Castel Gandolfo, Franz Ehrle, the same Vatican library prefect who later bought the Jesuit books, warned the Jesuits of the impending danger of further confistations, and the Jesuits moved large collections of books out of the German College in Rome to a hiding place in Holland, pretending (again) it was part of the private library of the Father General.

As I already wrote before, people coming in and out the Villa Torlonia were registered in the diary. Voynich does not appear in there. The best evidence we have is that he never entered it.

How could he choose the books that he would buy?
Maybe he didn't.

We know from correspondence that he had a standing order of $100 for every single book that he could get.
Maybe Strickland just brought him the few that appeared interesting or valuable. 

I can even imagine that Voynich never knew the exact location of the hiding place, but I don't know that and it doesn't matter. He told De Marinis that the books came from the library of Henry Benedict Stuart in Frascati, and he told his wife in secrecy that they came from the Jesuits in Frascati.