Totally possible but I would have to defer and get more info from the other proto holders out there. the only provenanced proto xmetal I have is a juliet and it has not marks. there are others out there with marks but they are not serials, more like marking to see how the etching looks or how to track the parts with subtle differences.What if they took a serialized R1 off the line and used this pair as the first example for copper plating.
just throwing it out there.