I got 2 genuine Colt upper half conversion kit with the blue and white factory box last year around Sept. - Oct.
They were a CR6920-EPR CK M4 carbine and a R0901006CK A4 20 inch barrel complete upper half.
The CR6920-EPR CK Enhanced Patrol Rifle complete upper half with BCG and charging handle, latest Centurion Arms 13.5 inch with the latest black markings and no BUIS.
The upper receiver was marked M4 by the front gas tube hole, it have extended M4 feed ramps, the barrel extension is M4 feed ramps, the upper receiver, barrel and charging handle are marked with cage codes.
The bolt carrier of the EPR had a (looks like hand marked) small letter C and the bolt had very faint hard to see the MPC marks (I had to remove the lube and use a magnifying glass to see the markings).
The other upper half is a R0901006CK 20 inch barrel A4 with Magpul SL rifle handguards, no rear sight, BCG and charging handle.
The upper receiver have no cage code, only square (Brass Aluminum Forging Enterprises) forge mark, no extended M4 feed ramps, so this is a rifle upper receiver not an M4 carbine, but with M4 extended barrel extension (should work OK). No cage code on the charging handle.
The barrel had unusual markings because it had no cage code, no mfg date, no supplier marking letter, marked with letter C and the M & P marks are apart, not together.
The BCG markings of this A4 rifle upper half are the same as my CR6920-EPR M4 carbine upper half.