Why did they have to keep checking the book?

In my mind, I would be certain that Phoebe would have the entire book memorized by season one or two so why would they always have to check it as if everything was some big mystery. It’s a large book but not that large especially if they read it everyday and it’s their legacy and lineage. With how Phoebe was nerding out on it at times, I’m certain she would have it memorized.