C/RC over the first position is the most common encountered, it is for the hardening of the receiver. Some firms, like Danzig, it was almost used as a final acceptance as it is rare to find a mid-war that doesn't have a C/RC over the first position.
Simson too had a thing for C/RC parts, but it is very common to see C/RC parts on wartime production. Basically means the part failed to meet the inspectors standard and the parts were passed for the revisions to accept. I doubt it was nearly as formal as all this, far too common to see, and what is known of acceptance, especially of small parts, suggest it was all done in large lots (as was typical in the US military also, - whole article have been written on US Army lot inspection, the practicality and safety of the procedure... Storz barely mentions it but does briefly.)