Rob's 'C' seems to have taken some 'licks', just as mine had. It makes me wonder how those extraneous rocks that hit those 'C's .. always hit the C rather than the B, U, etc…?... OR maybe the diff factory put those 'C's on the rears – of the late 69's, and then decided to 'remove' them, and banged them up at the factory intentionally? (I think no one knows the real story or reasons for that – management made an unprecedented decision to continue production of '69 Camaros and Corvettes for an additional 5 months… so obviously things were in flux and decisions about '69 vs '70 issues made quickly ...)..
Rob's 'C' has the same relative spacing before the BU as mine does… almost all the 69 rears with the C.. the C is displayed a couple of character spaces to the left of the 'BUxxxxGy' code.. it's almost like they didn't want it to be considered part of the app code? Is the 'C' used on 1970 3 letter diff codes displaced the same way? Or are they closely spaced as if stamped at one time?
PS. Why don't we consider the 'E' as part of the app code as well? ... 
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The "hits" are more than likely just coincidence, based on the location on the axle tube. They are not an attempt to remove them, at least not by the axle plant or assembly plant. And those are not the only ones I have seen banged up.
The 1970 codes are similar, with the C being spaced over. There is at least one example of that in the axle thread, and I have others.
E is part of the code, but is only there to designate which limited slip carrier is installed inside, E being for Eaton.
I will see what I can find in the Chevrolet Service News documents I have, but the three letter axle codes were planned, not just done on a whim.
Added - I will look again tomorrow for the September/October 1969 CSN that may have notes on the 3 letter axle codes.
