It's been a while since I was really paying attention to this but "production order" puts scores OUT of the order they were recorded in.
e.g. Corbomite was recorded AFTER Charlie X, The Naked Time, Mudd’s Women, and The Enemy Within.
That's because the score is just about the last thing done, after the editing and effects have been completed -- otherwise the composer won't know what he or she is scoring to. And as Harvey
said, "Corbomite"'s effects work took a long time to complete, which is why it was aired so late in the season.