Originally Posted by
nitmr26
Colt released the 6940 in 2009 and the 6940P in early 2012. Colt's 2012 catalog has a picture of a 6940 without the insert next to a 6940P with the insert. I purchased a Colt 6944 (6940 with 14.5" barrel) in November of 2012. It does not have the insert. I've seen pictures of another 6940 that was manufactured in 2012 and it does have the insert.
Granted that's only a few data points, but it looks like the insert was added to the DI 6940 upper receivers at some point in 2012.