Agree with this. However, I find the letters ABC to be a bit imprecise as their may be a range within each level/letter. Just did a runthrough on some of the pieces from the last auction with a 3 category ranking (1-10). Obviously this is subjective but I tried to tie values to at least what the market looks to be rating each category. For a piece such as the KJ page, looks to me like whatever the buyer ranks the quality of the page would determine price it went at and this buyer rated it at least on the higher end of B (4-7). Anyway, it was a fun exercise for me to get an idea of why things might be priced a certain way and probably would help me to allocate my future spending.
Full disclosure: guessed a bunch on many silver age pieces because I don't really have a clue why certain arcs or runs may be important.