Most vintage Swiss pocket watches did NOT have serial numbers and can't be dated by this method. Some American watch brands did not use a consistent series of serial numbers, but most of the big manufacturers did.
Not all vintage watches can be dated using the serial number. You should consult the serial number table for the specific brand of watch movement you are trying to date by selecting a company from the menu on the left.
The example below uses information from the American Waltham Watch Company, but that is just an example.
