I heard that in the books Cody and Astor are taught the code by Dexter as well. Don't know about Harrison but with the way his mother died he would be a logical choice (using Dexter's logic) to teach the code as well. Don't know how that storyline would play for me so that's why I was glad when they were sent away last week.
Thought about getting into the books but heard, as you said, they were far different. I enjoy the tv show so much I didn't know if I'd enjoy the differences as much in the book. Now you have me interested again.