A39 and A85 were not 1969 Camaro ordering codes for belts. They were options, but transparent to the buyer, and not used for ordering; they were used in prior years (67-68). The 69 YA1/2/3 ordering codes, which appeared on the WS in place of the actual option, allowed the dealer not to have to worry about the various permutations of deluxe and standard, front and rear, shoulder and lap, so that the correct belts would get into the car without a RPO screwup and the order being rejected.
To Lakeholme - you might want to refer people to the CRG decoding page for POP decoding. It has the latest accurate info.