What I understood is that holes at the end of the frame tube were there to vent out expanding gasses during heating and brazing the frame together so as to keep the epanding gasses/pressure away from the area being brazed to avoid creating voids. bubbles or gaps in the brazing material. Not sure if they are always required as I've heard of some frame builders not needing them at all.....
BTW, some of the holes on campy dropout drive side faces were threaded and meant to support a "portacatena" chain hanger. A handy item when transporting bikes without their wheels on to keep the chaing from thrashing about, but I also wonder if it was worth losing the space (126mm) for the 7th speed on a FW sometimes..... I prefer a brazed-on chain hanger peg on the right seat stay instead because of that...

Chombi