I haven't had the opportunity to handle many originals... but in every photo I've ever seen of an original barrel out of the stock (where the barrel was pinned) there is a simple drilled hole in the lug. I've never seen a photo of an original lug that was slotted for pins.
Maybe they shot 'more shots' in a lifetime, i.e., a shot or a few every day, than we typically do ... but 'less per session' ... ?
In that way, they may have never noticed issues from constricted expansion.