Sometimes we get too narrow thinking about machines and model numbers. Singer did not change model number as quickly with earlier machines (like before the Touch and Sew group). Now days it seems Sewing companies change model numbers all the time, even if they just change the color on a dial.
If you looked at a 1968 Chevy Nova, you most certainly would not expect it to be identical to a 1972 Chevy Nova, but we do this with the sewing machines all the time.