Sergeant Carter Dates a Pyle - S2-E20
Other mistake: Private Duke Slater's utility uniform shirt is different from the other Marines. Duke's uniform has square pocket flaps with the button exposed, an exposed button front shirt and the sleeves do not have button cuffs. The other Marines' uniforms have tapered pocket flaps with a hidden button, a hidden button front shirt and the sleeves have button cuffs. (00:05:00 - 00:06:00)
Answer: If you saw the whole series run, you know that Gomer was a country bumpkin. He fumbled, stumbled and tumbled his way into one disaster after another. There was an episode that questioned why he was never promoted. However, a few years before Jim Nabors died, the real Marine Corps, gave him a ceremonial promotion to the rank of Lance Corporal, which Jim gladly accepted.
Unfortunately, I never saw all the episodes. Only a few episodes and a clip of the episode where he sings "The Impossible Dream" which made me wonder why he was still a PFC. Thanks so much for the info.