BJ is a standin for Trapper John!
Clue is in part 2 of 6/1 epsiode "Bug out" a the end BJ is longing with Hawkeye sipping alcohol- takes place at during the in Battle of Uijeongbu of June 25-26, 1950 when the US Forces "bugged out" down to the Pusan periminter-fact it is a remake of 1/1 epsiode "M*A*S*H the Pilot" which also shows Trapper John with Hawkeye sipping alcohol being Korea {June 1950}! Yet BJ came to Korea {4/1} a week before Potter came in Sept 1952{4/2}!