Except that the question got raised right back up again in "Trials and Tribble-ations", also DS9, where the DS9 cast ended up in "The Trouble with Tribbles" ToS episode- quoth O'Brien, upon seeing the Klingons in the DS K7 bar:
O'Brien: "Those are Klingons?"
Worf: "We... do not speak of it."
So... uhm... yeah.