Yes, vent holes for when the tubes are heated for brazing the DOs on to the stays and fork ends, same at the fork crown and at the rear DOs.
Back in the mid 80's, I also used the holes to fish through my Avocet 20 bike computer wheel sensor wire from the brake caliper area, into the hole on the top of the right fork leg, under the fork crown, down inside the fork leg and out the hole just above the the right front DO, connecting to the magnet sensor mounted to the DO.. No visible ugly wires going down the fork leg for me back then.....but now I just have wireless.....
Chombi