Hey Mia,
I use CGP revision guides for each of my subjects and I closely study the specification whilst using them.
It depends on the CGP book, but in my own personal experience I do find that details on the specification are not always present in these books, however, I stress that this is a very rare occasion.
To be honest, You will get above a 7 if you read the specification in conjunction with the revision guides, anything omitted by the guides is easily picked up as you read through the spec.
Best Wishes,