The key words utilized in the preparation and then again in the activation phase of PR are analogous to pebbles that are laid to mark a footpath through the underbrush. If the trail is not regularly used, it become overgrown, the endpoint is still there but the path to get to it is obscured.
If the information in a particular book or preferably a group of books is important to you, then one need to construct more permanent roadways in lieu of the footpath. How? Memory mapping, content mapping, spelling your keys words backwards in you mind, ABC list, mnemonics, image streaming, cross reference it to other information in your mind, probe, probe, probe … accessing and utilizing the information.
Take a look at the Memory Optimizer course http://www.learningstrategies.com/Memory/Home.html The combination of the Memory Optimizer with PR is a great combination.