In the episode "Be Careful What You Witch For" Phoebe is looking at a book while talking to the genie that they had released in the attic. Now the book she was looking at is entitled "Witches". I found that book at Borders book store and not a single word of that book had to do with genies.
Most people wouldn't catch that, unless they go to a book store to check it out. And maybe phoebe didn't know this. And maybe she was bored, so to take a break from the BOS, she picked up the book to read about herself. :-)
For each episode (or for each new demon, warlock or whatever), they add a new page to the Book of Shadows. So when you found that other book, they didn't have the one about genies because The WB or the writers or whomever added it to the book. (The Book of Shadows is very valuable and I don't think it is for sale, or at least not until the show is over in May 2004.)