Continuity mistake: When Klink is talking to Schultz, his monocle is in before he bends down, missing when he's looking at Schultz, and back when he straightens up.
Continuity mistake: As Schultz is going to get checked out, Hogan and the boys stop him, and Hogan feels Schultz's neck. Schultz's arms are by his sides, then after the angle change, they're by his hips. Also, there's two men walking behind the group that weren't there a second before.
Continuity mistake: When Klink is talking with the doctor, he sits while reading the report. One moment, he's holding the folder, the next, his hands are folded without having dropped the folder.
Continuity mistake: As Schultz comes in, Klink has his left hand on his forehead. As Schultz is talking, Klink starts to raise his head, his hand very close to his forehead. When the camera cuts to a close up, his hand is below chin level.
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