<400 Total for USS Farragut, 11 Years Prior to TOS [as per] "Fortunately, I read somewhat faster. In brief, Doctor, nearly half the crew and the captain were annihilated."
Actually, that's >400 because 200 is not yet quite half of it...
It would seem that all figures for Kirk's vessel markedly differing from 430 are rough estimates or downright errors made by uninformed people.
Although Anan's figure might be an estimate, he did have good reason to have an accurate count for reporting to the death chambers plus Ambassador Fox might have had a large delegation with him pushing the number to 500.