Other mistake: As Hogan and Kinchloe sit on the bunk to keep the trap door from opening, the secret switch to activate it is visible.
Continuity mistake: When Klink is "taken hostage" in the barracks, he is in his tunic only. Later in the car he has his overcoat on. He was supposed to be kidnapped, he could hardly ask Hogan to let him slip into his office for his coat.
Answer: Nimrod's actual identity was never revealed in the series. It was only known that he was a British intelligence agent. Nimrod was not Colonel Klink. Hogan had only implied it was him as a ruse to get Klink returned as camp commandant, not wanting him replaced by someone more competent who would impede the Heroes war activities. (As another contributor previously posted, the term "nimrod" is slang for a nerdy, doofus type of person, though it's unclear why that was his code name).
raywest ★