I've an Indy 500 flyer and just read it over and there is no mention of "diamond plate" but having said that I quick checked some other flyers I have for the same era of B/W and there is no mention either. The last sales pitch on flyers and the barcoding thing I can see is about '92-93. Maybe it was just an oversight in advertising and it was always done but was never thought worth a mention after awhile as it was a "given".
