It makes sense to open up the pipes, I wouldn't want to have to miter around the internal fillet. The number of people making lugs is fairly small relative to the number of people doing bilaminate construction. For bilaminate, I don't think people generally join frame tube to frame tube. But everybody makes up their own method, it's not like there is a consensus technique.

The owner of speedplay wanted a Masi replica, and the builder made lugs. I think they were welded. The funny thing about that was that there is a really good Cinelli lug copy available, and I'm pretty sure it was available at that time.

Well before the internet era, I wanted to modify some lugs by adding parts. So I welded tube scraps on to them -- cleanup was a real pain. Fast forward 27 years, and I saw pictures of Peter Weigle modified lugs where he brazed extra parts on. It was a real head-slapping moment. My point is that now we can go get ideas from others (and also, my first impulse is to do things the hard way).