It would be intersting if anone has started gathering serial numbers and compared the Japanese models. The large export of Japanese machines began after WWII, and before that time I guess there were 15 clones in production. The very early Pine models look more like the European 15 clones, with the type of stitch length lever you find on Pfaffs and Husqvarnas. The European 15 clones had reverse lever by 1920s and some could drop the feed dogs too. It might be the reason Japanese clones incorporated these features on their machines after WWII. I guess the typical Singer stitch length lever with reverse appeared after 1954 when Singer bought into the Pine company?
You can't go by the "deluxe" badge on the early Kenomores, at least not alone. You will find all kinds of referance words like "deluxe", "automatic", "-omatic", between brands all of the 50s and 60s, not just Japanese. The 1930s Kenmores were US made, often rotary hook and race. The Japanese probably borrowed the words from existing names and brands. They largely aimed for the US marked.