The most useful patent information is found on the razor itself or on instruction sheets and packaging. Patent numbers or dates found in these places indicate the earliest possible date for the item. Regular (utility) patents expired after 17 years. Older design patents were good for 3, 7 or 14 years (now they are only issued for 14 years). An expired patent is usually no longer listed on items. For example, a patent date of 1903 means that the item was produced after 1902 and probably before 1921. Beware! Exceptions do occur.

     The mark Pat. Appl. For would at first seem less useful than a date or patent number, but if one can locate the patent referred to, it narrows the vintage of the item to the time between the date the patent was filed and the date of issue (plus a year or so). The false use of phrases such as "Patent Applied For" or "Patent Pending" was and is illegal, but a patent that was filed for may or may not have been granted. An existing patent doesn't always mean that the item was manufactured and sold. Physical evidence is required– a razor in the hands of collector, a catalog listing, an advertisement, even an instruction sheet or empty box would suffice.

     A trademark listing that states that the trademark was used for safety razors (not just for razors or cutlery items) is probably also proof that at least some product was made and either sold or given away. Trademark listings sometimes include a used since date but that can be misleading since it may include prior use on other cutlery items by the present or previous owner of the trademark. In the absence of a used since date the only other clue is the date the trademark application was filed with the patent office.
 

From Safety Razor Reference Guide
by Robert K. Waits © 1990.