Hi Prynceska,
I'm glad I can help. 
You stated "The theory of "once it is in there, it is in there forever" doesn't gel with me. This seems to suggest that the subconscious mind can never forget. Can that possibly be true? Is our subconscious mind hanging onto every single memory that we have ever had?"
I saw a program on TV some years ago, about some research that some doctors were doing on the human brain. (I think they were attempting to map the brain at the time.) When they were doing brain surgery (during which the patient had to remain conscious), the doctors would very delicately stimulate different parts of the brain. What they found was that if they stimilated areas that had the function of storing memories, the patient would perfectly remember and re-experience things as if they were reliving the experience all over again. They had perfect recall of things from around 2 years old to when they became an adult. The doctors conclusions were that everything you have ever experienced in your entire lifetime is perfectly stored somewhere in your brain. Under the right circumstances or conditions it could reach your conscious mind.
Now having said that, in my own opinion, if I wanted to activate a book that I PR a year ago and haven't touched since, I would sit down and PR it again to help refresh my conscious mind as to the content and layout of the material in the book. This would make activation a bit easier.
As far as the plasticity of the brain, my own opinion or theory is that the memories are permantently stored and our conscious access to those areas of memory change with time depending on our demand or need to access that information over time. I do not know for sure because I haven't looked into this area of research in a very long time. I just might have to do that with syntopic reading once I get a handle on how do that.
Anyway, I think that answers your question. If not ask again and I will try to help if I can.
Sincerely,
Gregory
