Are all of the filters made by Champion stamped "AA". I was going through some of the ST filters at Wally-World and found that some numbers are indeed stamped "AA" while others are not. The ones that were NOT stamped felt lighter and looked different in construction. Just curious, is it possible that Fram has moved in and are making ST's now? Gee, they'd make a killing off everyone who now buys the ST instead of the Frams. Just food for thought...