I have several old machines, I had found the serial numbers and were able to date them, but how do I know which model they are, if it is not on machine. For instance, I have a Singer treadle with serial #F8014464, which I have dated as 1917 but would there be a "model" for it? Also, have a Singer with serial number G0891901 but again I do not see a "model" name on it. This may be a dumb question but I am trying to learn. Thanks for any input.