The lightweight models announced in 1938 pre-dated electro-forge welding by 3-4 years. The first electro-forged lightweights were New Worlds of the i-series serial numbers in 1942. The move to electro-forging did not happen all at once. I-series New Worlds sometimes are fillet brazed and sometimes are electro-forged during the course of 1942. And among those that were electro-forged, it was only some of the frame joints, particularly those that particularly lent themselves to the process. Some joints that were more difficult for the process remained fillet brazed well after WWII. The process was revolutionary when it appeared at that time, but by the 1970s was a pretty dated way of building a touring bike. They were durable though, that's for sure.