During the Korean War, a point rotation system similar to one established during WWII was used to decide who would be rotated back home and discharged. A total of 36 points was required for a soldier to earn rotation back to CONUS (Continental United States); 4 points were given for each month in a combat zone, 3 points for being located between regimental headquarters and emplaced batteries, and 2 points for rear echelon duty.
Jamie Farr is the only regular cast member who doesn't appear in the Red Party scene. In fact he only appears at roll call in the begining and at the episode's end, and it is clear his one line is filmed on a soundstage, not on location with the rest of the cast. In wide shots, Farr is clearly not there.
To help establish that his new "cheesy" mustache isn't going away anytime soon, Hunnicut draws one on his surgical mask in the O.R.
At 23 minutes in at the Red Party, Alan Alda really does crack up laughing when Col. Potter brings him a drink. Harry Morgan says, "Here you go, son," and Alan loses it at Harry's appearance. Harry continues, "Boy, you made the bonehead play of all time," and very nearly doesn't finish the line for laughing so hard; but he recovers-- "But you sure did something for this motley crew."
One of the series' regular extras, a redheaded nurse usually referred to as "Gwen," is visible in the Red Party scene, and she has somewhat redundantly had her (genuinely red) hair dyed bright red just like everyone else.