C/RC can be found on any component, stocks are less common, but receivers often have them, usually under or above the first position (hardening of receiver). Danzig it is very common, most have a C/RC 1916-1918, and yes it starts to be "common", most common actually, around the k- block of 1916. Prior to that period, it is less common and in 1915 rarely seen.
Danzig is not alone though, C/RC can be found on any maker and any component, it is a correction, Görtz would have the exact meaning, but it essentially means that the component did not meet the standard but was deemed acceptable.
Simson also had a lot of C/RC on their production, I doubt they made a wartime bayonet without one... not sure of their pre-war bayonets, I have only owned and seen a handful. It is a common marking on wartime production.