They did produce a very few- Dennis Todd confirmed this. I actually have one- Bought it years ago. It was somewhat used but I _think_ its the real deal- "M4" above the cloverleaf and not a black one moly coated/ Norrell coated.
What Ahab is describing by saying the "cloverleaf" is the milled hole pattern where the gas tube goes thru the front of the receiver. Most M4 uppers (not all) have either a "4" or an "M4" stamped above the hole.
I just bought a RAS numbered Colt M4 Upper, stripped, from Paul at MSTN. It is as close to a perfect match as you can get for my Preban Sporter Match HBAR. Of course a RAS numbered upper is going to run you a little more. -M4_A3
It takes a big man to cry...It takes an even bigger man to laugh at him.
The Department I work for has some R6721 AR15A3 Tactical Carbines with the A3 (detachable carry handle type) uppers with the M4 stamp on the front, feed ramp cuts and finished in the Colt Gray from the factory. I believe these weapons were made in late 94 and maybe early 95. One of them at least is a 3 digit serial (post ban).
I have a Colt factory original R6850DC 7.62x39 conversion kit that is built on a gray M4 flat top upper receiver. It has a "4" stamped above the cloverleaf along with the enhanced feed ramp cuts. I believe it was manufactured sometime in the mid-90s. The finish is a good match with the gray pre-ban Blue label R6830 lower reciver it is mated with. This upper receiver also has "COLT 7.62 X 39" stamped on the left hand side, so for most it probably isn't the most desireable for use in building up a 5.56 M4 type. Looks and works great as my 7.62x39 tactical carbine, though.
I originally had a 1:9 LE6920 Colt M4 conversion kit that I bought new from Hoplite. It was great but being a late model it was black. I traded it (+$) for a 1:7 original Colt dark grey M4 upper with RAS t-numbers from Prideboss here on AR15.com, BTW he was great to deal with.
It's not a perfect match with my pre-ban light grey blue label Sporter but it's pretty close.
Here is some PICS. Colt M4 with T-numbers and latest Colt ribbed stock
Thanks to everyone who replied. Aside from barrels and feed ramps, what difference is there between the upper on a 6700 and the uppers pictured above? The numbers on the rail? I too want to match my blue label lower with an A-3 upper.