Thank you - do you know what a 12 without a C in a diamond cartouche means?
Clarification: Do you mean just 12 all by itself, or do you mean 12 in a diamond but no C? If the former, that's simply the bore designation. Means it's a true 12, bore diameter .729. Quite a few British 12's were either somewhat overbored or underbored (much more often the latter, from what I've seen) and you'll often see them marked with bores other than true 12. If marked with a 13/1, for example, that would mean a bore diameter of .719.
I can't recall ever having seen 12 in a diamond but without the C.
