For now I don't think "Crucible" would be stamped after a tradename/type steel; therefore, "C" would be for Cumberland and Cumberland of Maryland. But it is odd that one might be for a city while the other is a city/conglomerate/company(it might be the company was named after the city within which it operated?). But I do think that SB&Co. was a brand/tradename/type/variety of steel. It might be in the U.S. patent data.

Kind Regards,

Raimey
rse