FWIW, Draco in Sally-Anne's biting book post suggests that "a" biting book is something you can make just to show that you can. So, there might be more than one, it might not be Monsters, especially if Hermione is good at making "special" covers like she did with Slughorn's potion book. I admit it's a reach to tie Sally-Anne in, here, but I'm leaning toward "not disproven." :)

the players are doing a fabulous job of layering in plot details that may seem irrelevant in their moment of mention, but which are beginning to have significant pay-offs

Most definitely. Which makes it great fun to be a watcher.