OK .... well, I don't know about Alan but I've been confused from the start! The OP said "I've noticed that on several AA flights, the only available inventory booking classes are C, Y, B, M, V, K, and Q." AFAIK, AA does not use C as a "booking class" - it's a hidden inventory class used for VIP upgrades, so you're never going to see it alongside Y, B, M etc. D will never appear on a domestic AA flight and the only flights that will not show F or A are single-class Eagle flights. I was unclear (and still am) whether the OP was referring to flights that had zero availability in A, D or L (as the case may be) or flights that simply did not have those classes at all.