Just wondered if anyone could tell me if Colt assembled any non T marked flat top uppers for military use or is the non T marked M4 Upper just a replacement part only . The reason that I ask is that I recently came across a Colt M4 flat top upper marked C A behind the brass deflector and marked M4 above the gas tube. It had the SOCOM heavy M4 barrel with an M16 bolt carrier that lacked the T markings. Thanks in advance for any help.

Quoted: Some Colt uppers do lack the T-markings. IIRC, all current production has them.

False,

All USGI now have T numbers.  

The current batch of comercial uppers that came out of Colt doesn't have T markings and they are C keyhole marked.  Comercial weapons may or may not have T numbers

T numbers came out in 1998.  

you are correct