It’s very simple. I rate books such as the Dragons in Our Midst books older (mid-teens plus) than they are supposed to be (pre-teen and teen) for several reasons. One, is that a lot of the time, I find that the automatic rating system really isn’t suitable. For instance, Inkdeath is supposed to be a children’s book. My mom and I were both shocked. The book is clearly young adult, NOT suitable for children, (heavy cursing and Orpheus is entirely innapropriate with some servant girls). I rate it as I think it should be rated – the way we would read them here at the house.
Because lots of times, I think publishers were kind of crazy putting their age ratings up ^_^ I hope this clears everything for you. (Even if it was sort of jumbled). :D