The salt vampire and the frowning long-faced alien always creeped me out as stills behind the closing credits but I wouldn't know the stories which went with the pictures until quite a bit later, when "Man Trap" and "The Corbomite Maneuver" were shown as between-season reruns.
I'm sure you saw "The Man Trap" as a re-run, but it wasn't shown "between-seasons," as you remember it. Indeed, "The Man Trap" was never re-run on NBC during the show's first run
. You must have seen it later, in syndication.
"The Corbomite Maneuver" did get an NBC re-run, though, on May 11, 1967.