Knocking out a guard obviously makes a lot more noise than shooting him, even though its supposed to be the stealthier way. The game's explanation is that other guards can hear him groan when shot, but they don't seem to hear the noises made when you knock him out (he still groans, and then hits the floor rather hard).
The U.S. soldiers in the Abbatoir level have the flags on their uniforms backwards. They're supposed to be with the blue field facing forward. Also, they're missing the nametapes that go above the chest pockets.
After Wilkes is shot, the V-22 Osprey is seen to be in Russian Airspace. Russia is a little over 5600 miles from Langley. The Osprey has a cruise speed of 277 MPH, meaning Wilkes would have been bleeding in the back of the Osprey for 20 hours.