Along those lines, I've occasionally wondered quite how, and when, Benton found out/was told/realised that the tall, arrogant chap working as the Brig's scientific adviser was the same person as the short, funny chap he'd met in passing during the International Electromatix business, not just someone else with the same call sign/codename.
Must have been a bit of an eye-opener, possibly explaining why nothing ever shocks him again, and why he's far more of UNIT's inner circle than his rank would dictate.
Benton was always a perceptive fellow. He tended to figure things out a step or two ahead of the Brigadier and have less trouble accepting them. So if the Brig could understand that the two Doctors were the same man, Benton would have no trouble with it.