It's my understanding that the Moultons had an open format, two numeral year code stamped on the seat tube, on the opposite side from the serial number. Sometimes, there is a single character, alpha prefix designating the factory. Even, if you find the year stamp on the frame, it is still worthwhile corroborating against the year code of the hub, per Randy. Once we have the year and pictures, it should be relatively easy to determine the model.