Col Potter commanding, visits a soldier in the ward writing home. He's dated the letter September 12, 1951. When Col Potter is assigned to the 4077th, the announcer stated the date of his arrival September 19, 1952, a year later.
When the injured soldier is placed on the litter on the helicopter to be evacuated the toes of his boots are very scuffed. Upon arriving in triage his shoes are fully black and quite shiny.
When Prvt. Rich writes forgot anniversary on the paper the h in call her goes from a lower case to an upper case h. Also the f he writes moves to the left a bit.
When Pvt. Rich is placed on the chopper, the clear (although very dirty) cover being placed over his head is not shown. When the chopper is coming in to land at MASH, he appears to be looking through the front of the aircraft but not through a cover. When the chopper lands, BJ pulls the cover off the aircraft.
When Margaret is putting her right hand over Pvt. Rich's eyes and later when she's giving him a sponge bath, Loretta Swit's fingernails are seen to be over an inch long. No nurse, especially a head nurse, would have fingernails that long.
What the audience sees is what Pvt. Rich sees. But the camera keeps turning at odd angles for someone lying down, and for someone with a severe throat wound. Pvt. Rich's head wouldn't have been able to move that much.
When Hawkeye sits on the bed to talk with Pvt. Rich near the end of the episode, he takes up nearly the entire width of the bed, meaning that he would be sitting on top of Rich's legs. Obviously there is no one lying in the bed.
The clouds of dust raised as the chopper lands and takes off are obviously an optical effect as the action keeps moving as the individual whiffs of dust stay in place.
As Pvt. Rich is being flown away to the 4077th, he has a clear view of the ground. If a 'bubble' had been secured over his head, the view would be obscured, dirty. The camera has been attached to the side of the litter, instead of at the head.
Pvt. Rich is wounded and has his injuries assessed and is immediately placed on a litter. It's highly improbable that an infantry platoon patrolling alone would carry litters with them as patrol units carry the bare minimum to allow for mobility.
The talkative patient to Pvt. Rich's right in the post-op ward can be seen holding a paperback novel ("Visiting Nurse", by Margaret Howe) which was published in 1959, six years after the Korean War's end.
Colonel Potter tells Private Rich that he makes a point of meeting every patient that comes through the 4077th. Considering the number of casualties they get, this would be impossible.