Totally agree - back in the late 80s I was working on a lot using black book to price trades and selling using NADA.Back then, the N.A.D.A. was the bible. That was compiled by dealer and auction reporting in your region.
Both of then also used the "Black Book" auto values. Black Book was always lower than N.A.D.A. We would buy with Black Book and sell with N.A.D.A.:lol: