interesting that list leaves out Russia , I read there was also a plant in norway.
my very most favorite treadle is early 15 - ? no motor boss. next 15 on the list is elec seem like a 1945 or 54 maybe a 88 or 90 ? has reverse external motor , it was very unused, anyway it has never stalled on a seam, most of my type sewing is heavy thick fabric's
never seen singer list a 15 as an industrial, they did right around the turn of the century start with a 16 industrial, that's is pretty much just a big 15, they use the same bobbin case and bobbin
singer made to many machines to keep up with . I don't even agree with a New family being a 15 model, only thing alike is that the upper tension is on the face plate