"I then concluded that the same must be true for code."
I think it's true in many areas. I often look back at things I've done (including writing code, proving theorems, etc), and sometimes I realize that I really had a shallow understanding of that which I thought I understood well; sometimes, though, I'm surpried that I had understood something so well and wonder how I managed to do that. I do often go back and review things many times (e.g. reading the Camel book or others I've studied in the past.) The only problem with that is that is takes time from going on to new things - there's only so much time allotted to each of us - how to spend it is a puzzle...(hopefully one doesn't waste some of it trying to resolve that!)
chas