This is all from memory but there recently was a group 20 to 50 Mapes on Ebay. They were stamped, but I believe it was a different letter. I believe they were stamped “B” and the seller was implying they may have come from the Borland collection. With the abundance of Mapes chips, would it be possible there were used in an illegal game. Would be cheap and the Hot stamp would identify any outside chips.