All of your observations are spot-on with what I see under magnification - the black dot is definitely out-of-round and that exposed bit looks like filler, but why use white filler? The 'C' is also crooked. Maybe these were ongoing issues, and why they abandoned the 3-part 'C'?
Any chance this is a replacement stem and someone tried to replicate/emulate a three part C, or put a home made C in an original stem where the C came out?