Makes one wonder - I suppose they cut the hole and then bound the opening by hand - I've got a few vintage clothing sewing technique sites bookmarked, would love to do that, but I know I never will, too many other hobbies and I won't live long enough to do them all LOL!!
I use to feel differently when I was 20 years younger, but now I'm trying to cut back and stick with only a few things - but sewing was one of my first loves anyway.