The score scaling is obviously not going to be the same for TBR passage passages and AAMC full length tests. I got a 70% on a chemistry test during the school year and it was considered an A. If I had gotten that same % in my physics class, it would have been a C. Do you see how this statement has logical fallacies?
FWIW, the scoring on TBR should only be used as general guidelines. I think it is kind of inaccurate in certain sections/chapters. Overall, it probably correlates to your actual score (if you do well on TBR, you are likely to do better on AAMC, DUH!), but the actual numbers, don't mean much. The score conversions in TBR have very little significance, so just disregard the scoring. Just try to use the books to learn. Trying to gauge what level you are at using those scores is pointless. Its like trying to do a buffer titration with a broken pH meter. You have a general idea where you are at, but there is a lot of room of error.