I have a box of old Hetchins lugs, that spans the era where sand-cast lugs were giving way to formed sheetmetal, welded lugs, so some of them are cast, some welded. The cast ones are the coolest but definitely require thinning. I think the older casting process didn't allow such thin fine features — molten steel might now flow all the way into the thin parts? So they had to start out thicker. They were also machined on the bores for the tubes, so the fit is very nice. But some of the bores are a bit off-center relative to the cast outside suface, so the walls are thick on one side and in some cases vanishingly thin on the other. I assume that's why these lugs survived — they are seconds that were not considered good enough to make into a frame.