Other mistake: When the Heroes are outside talking, the camera focuses on Col. Hogan. Over his right shoulder you can see a hill with a baseball field's home plate fencing on top.
Other mistake: As Schultz goes to stick a pin in the map, he supposedly hits his finger. But if you look closely, he actually stuck it in the map at the very tip of his finger. This is clear because he didn't move the pin at all.
Other mistake: As Schultz tries to find Flensheim on the wall map, what he's checking isn't a road map, but a city plan with a harbor on it.
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. The term "nimrod" is also slang for a nerdy, doofus type of person, though it's unclear why that was his code name.
raywest ★
"Nimrod" is originally a king and hero mentioned in the Tanach and taken into the Bible and the Koran. His name is often used in the sense of "stalker," "hunter," and sometimes figuratively as "womanizer" as in "hunter of women." I've never seen it used to denote a nerdy person, and although I cannot disprove that connotation, I think given his role, the traditional meaning is more likely the intended one.
Doc ★
It's widespread enough that Wikipedia has an entire section on it: https://en.wikipedia.org/wiki/Nimrod#In_popular_culture