The Book Switch Theory

[Jorge_Stolfi]

PS. There is also the possibility that, between 1700 and 1911, someone with access to Kircher's correspondence and/or the Jesuit book collection noticed Marci's letter, and, realizing its huge monetary potential, pilfered it and sold it secretly.   At that point the letter may or may not have been attached to a book;  if it was, that book ("BookX") may or may not have been BookA, and in either case it may or may not have been MS408.

All the best, --stolfi