I noticed each time you open one of these books it says "Map updated." Does anyone know for sure what this book does, what it adds? I noticed it has said that each time I open the book and I'm not sure if it's adding anyhting new or just adding the same thing over and over?

It adds a few locations, such as the guardian stones, I'm not sure of much else though.

It adds two or thee guardian stones. If you read the book it mentions which ones specifically. (Shadow stone is one, I forget the others)

Warrior/Mage/Thief, Lover, Shadow and Ritual.

It will always say "Map updated" even if you already have them on your map.