Keep in mind, that the expired Singer patents that the Japanese HA-1 (clone) was designed from, had the second thread guide on the face plate for bobbin winding. Specifically, the Singer 15-30 had the second thread guide, and I don’t know for sure, but I suspect that the 15-30 patent was the one used by the Japanese. If not, it was a Singer model very close to the 15-30. While the Singer model 15-80 had a spool pin down on the deck, it still had the second thread guide on the face plate. By the early 1940s, Singer had completely re-designed the model 15, including a completely different hook assembly, and the face plate bobbin winder thread guide was not present on the model 15-88.
CD in Oklahoma