Yo,
Yeh, i'm sure you could pass the exam without opening the book (well, if you're lucky anyway!).
But remember the bigger picture... and why you are learning it.
At my recent interview with an airline I was asked a number of air law questions, and you can't turn around and say "sorry, that wasn't on the database!"
So whilst you can prep again before an interview, IMO it helps to get a foundation knowledge down in your head prior to revising when you get the call.