Was your Prestige account converted from a Chairman card? It seems more likely that AA is an internal code referring to the discounted annual fee paid by former Chairman cardholders. (My card was converted from Chairman MasterCard, and I do see the "AA" code.)
My ThankYou account is reflecting the same thing as OP cited-- the sponsor account is listed as "Citi Prestige AA" and in my points activity it comes up as "Citi Prestige AA Pricing". My account was not converted from the Chairman card (but I do have discounted pricing as a Private Bank client). This is a new change b/c I checked my balance last week and the "AA" designation was not present then.