Vergil hums in acknowledgement of his words about how exactly the sword was manifested, but he makes no attempt to try and replicate the potential spell or its results. He's not after just any blade, but after Yamato, and he cannot imagine a human unintentionally requiring a mundane blade through whatever means happened to be at play would produce those particular results. Even with great concentration and perhaps the infusion of his own demonic energy, Vergil wouldn't be able to produce the Yamato from any of those books. The conclusion results in a furrow in his brow as he closes the book.

Vergil holds the book out, offering to return it to the swordsman. But if he isn't interested in taking it back from Vergil, he places it in a free spot on the shelf regardless of whether it's the correct spot for it or not.

"You have my thanks."

Even if it didn't produce the results he wanted, Vergil is willing to acknowledge the exchange of information.