When Potter and Margaret are talking in the mess tent, Potter implies he was married when WWI started. In his first episode in season 4 "Change of Command", Potter says he joined the cavalry in WWI at the age of 15. In the season 10 episode "Pressure Points", Potter says he is 62, which would mean he was in his mid 20's when WWI started, which supports the timeline in this episode.
When BJ first comes to assist Charles in the OR, he calls for a pair of gloves, then clearly the nurse helps him put on the left-hand glove twice. The first time is more off-camera, the second time is clearly visible.
When playing poker, the table was limited to 6 players. After Charles' secret is shown, there are 7 players at the table. With 7 players, if, after the deal everybody takes 3 cards, that would be a total of 56, where a standard deck only has 52.
BJ says the acre of land at Stinson Beach he and Peg want to buy has "trees, the beach, a view of San Francisco, everything." But almost all of Stinson Beach actually faces to the west-southwest, with no view of any part of San Francisco. The very western end of the beach itself *does* face due south but, given the geography, would at most afford a view only the far western edge of San Francisco, which even today is itself mostly beach, park, and small homes and would be essentially indistinguishable from the rest of the coastline. The Golden Gate Bridge and other iconic landmarks are too far in from the coast to be seen from any part of Stinson Beach.
In reading the letter from Peg, B.J. says that he needs the $200 for the down payment on the house by the 15th, which is "today." However, South Korea is 16 hours ahead of San Francisco because it's over the International Date Line, making it still the 14th where Peg is. Because the down payment is certainly due on the 15th "San Francisco time," B.J. actually has until "tomorrow" to round up the money and wire it to Peg, and "tomorrow" being a payday, as B.J. mentioned, would obviate the need for B.J. to borrow the money from Charles.