Your premise is incorrect. THere are 256 total episodes, and Margaret, for example, did not appear in 11 of them, meaning her total is 245. Hawkeye should be 256. As for the others, I am verifying their episode numbers now.
It does say that it's based on IMDB. Wikipedia indicates 256 episodes and IMDB claims 251. Wikipedia counts "Welcome to Korea", "Bug out", "Fade In, Fade Out", "Our Finest Hour", and "That's Show Biz" as two episodes each. They were double-length episodes that were split in two for syndication, so 251 aired episodes became 256 episodes in syndication.
You're quite right that the numbers are wrong, though. Hawkeye was the only character to appear in every episode, being the only regular character in the Season 4 episode, "Hawkeye".
You're quite right that the numbers are wrong, though. Hawkeye was the only character to appear in every episode, being the only regular character in the Season 4 episode, "Hawkeye".