well, there's one on ebay... very rare! https://www.ebay.ca/itm/A-RARE-VINT...851375?hash=item48a466e26f:g:cK4AAOSwjghZxm~fPurchases made through these links may earn this site a commission from the eBay Partner Network
Oh don't say that Miki, I was just making some in the shed... I mean... discovering them... somewhere legitimate...
My guess is they found a few of these in 74/75 and they where service parts. Hence the slightly non standard-74 marking.
I just noticed the first ridge on the C1 caseback in MWO is flat. where as the ridge on the 74 caseback is more like the C2 in MWO sharp and pointed.