I had a teacher that worked for the publisher and talked about how they’d have a series of responses for people who wrote in for the part of the book where the author says he wrote his own fanfiction scene and to write in if you wanted it.

Like maybe the first time you write in they’d respond that they couldn’t provide it because they were fighting the Morgenstern estate over IP release to provide the material, etc.

So people never would get the pages, but could have gotten a number of different replies furthering the illusion.