After watching STAR TREK (TOS) ~ "SPACE SEED"
I noticed real fast that Sulu nor Chekov
was on this episode but later during the movie, STAR TREK II: THE WRATH OF KHAN,
Mr. Chekov knew all about the story of Khan, the SS Botany Bay and Kirk's decision to leave Khan on a planet from the television series. Chekov (Walter Koenig)
didn't come on the series until Season 2 and Space Seed was during Season 1.
So, I guess the reason that Mr. Chekov knows about Khan is due to the fact that he was off duty during television episode. Does anybody have any other ideas?