Fuel filler neck install

I know that the 70s and non-CA 71s had a vent nipple in the filler tube, which is why it has to be installed from inside the trunk (the filler tube and vent nipple won't both go through the quarter panel hole). I had thought since the 67-69 tubes go in from the outside without that nipple for vent that the cap was vented. Please school me if that's not right... where does a 67-9 tank get incoming air???