Vendors will continually call these C Mount unless they have been corrected.
weirdstuff-inc an eBay vendor, sold me 2 NOS Cosmicar 50mm f1.4 lenses, with 46mm pl filters, as C-Mount.
I have given him the bad news. As I am in Oz and he is in the USSA, no refunds are likely. He is otherwise a good vendor!
Perhaps this thread will fill up, making it more difficult for mistakes to be made?
Still may be worth buying, if you like vivisection!