L. Rauwolf

[ReneZ]

But we can be fairly certain that at some point between Widemann and Kircher, knowledge about how it got into Widemann's hands was lost.

I agree with that.
The possibilities are endless.
Widemann may have told Geizkofler who acted as the buyer for Rudolf, and he may not.
If the recipient of the book in Prague - Hans Popp - knew, well, he died within a few months after that.

There may have been a name or names on the then cover, which may have been lost in case it was rebound for Rudolf. Latest when it was rebound by the Jesuits in Rome.

It may even have been widely known when the book arrived in Prague, but nobody bothered to write this down. After all, we are very interested in this, but people then and there may not have cared much who was an earlier owner.