When I was at the library comparing wholesale prices in the Red Book vs. Black Book, which I assume should be apples to apples, the Black Book was always significantly lower, at least for the examples I looked at.
What was interesting was that the Red Book read like a "dealer-to-dealer" book. So wholesale was what dealers paid at auction, on average, and of course the corresponding "retail" values in the Red Book were higher to take into account reconditioning and profit margin, etc.
Black Book just seems like a marketing tool to me, made in conjunction with the dealers.
Appreciate the input artic.