I’m in the same boat. I was just pointing out where your theory falls short for me. No one would suggest that vents were sewn up for a functional reason. It kind of defeats the purpose of having them in the first place. So I offered a theory that made a little more sense to me, in that it would explain both sewn pockets and vents.
But I’m not a tailor either. I too would welcome a sartorial expert to come in and illuminate this issue for us. 