Hello WD
It is virtually certain that I welded your seat tab, pizootie tab (the little seat stay gusset plate) small bridge tubes, brake cable bridge, brake mounts, and rear dropouts. I welded nearly all of them for the Yo's made in Somerville.
I welded quite a few of the Yo main triangles and most of the Fat titaniums and road frames. I did not weld many of the forks however
We did not use vent holes in the tubes. On a rare occasion a weld would pop as I went to seal it since the heat would build air pressure in the tube. Most of the time I would weld almost all the way around, let it cool completely and then go back and weld the last little part to finish it. I would always do that in an area that could be easily fixed if it did pop.
If I did have to use a vent hole (more common on repairs), I would drill a 1mm hole somewhere around the middle of the tube and usually toward the inside or bottom depending on which tube it was, finish the repair or weld whatever the operation was and then I would use a quick silver braze to seal the hole and then sand it smooth so it would not show.
I was perhaps the only American Welding Society Certified Welding Inspector and degreed welding engineer who worked welding bike frames in those days. There could have been others working at the big guys like Trek or Cannondale but I never knew of any personally
Thanks for your interest!
Scott