Lost Manuscripts

For your consideration: an interesting article concerning books about books. Yes, The Da Vinci Code and it's foundation on the Gnostic Gospels is mentioned, but the author looks at the wholeb 'genre' of books concerning other books, both real and imagined. He cites Eco's The Name of the Rose as well as the Providence R.I. pulp legend H.P. Lovecraft:

And in some cases, an invented book takes on a life of its own. In the early 1920s, H P Lovecraft made several references in his stories to a book called the Necronomicon, apparently the work of a devout Muslim called Abdul Alhazred, also known as Mad Abdul. Over the years, Lovecraft explained that while he had “quoted” from the book, it was an invention.

Lovecraft's literary conceit was so effective that to this day deluded occulists persist in the belief that the Necronomicon is a real book.

N.B. Anyone interested in sampling some of Lovecraft's work can take a peek here.