Interesting info Steelsewing. I have not been able to get accurate details on the introducition of the 201. The earliest date I have read is 1928, but some give 1930 as a date too. I guess there were a few years of development, test productions, I just have to note down the best ducumentation when I come across it. There were definitely many years of overlapping in production of the various version of 15 and other models. I have come across late 28s too, with serial numbers dating production to more than a decade after the 128 arrived.