Waterman model numbers
The great majority of American-made Watermans from the hard rubber era that is, up until c. 1930 were marked on the end of the barrel with a numeric code that clearly identified the model. The basic system is easily learned, and runs as follows:
Note that Waterman changed its numbering system slightly at some point between late February and late August of 1917. The key differences on pens made prior to this change are as follows:
It should also be noted that stamping the full number only became standard practice in the fall of 1908. Earlier overlay pens will often be found stamped with two-digit codes.
There were some irregularities in this system (e.g., the #20, an eyedropper with a #10 nib), but things really started to get confusing with the introduction c. 1927 of the #7 and the #5, followed a couple of years later by the unnumbered Patrician and Lady Patricia. For a while a modicum of consistency survived: the #32 and #92 had a #2 nib; the #94, a #4. Then the #32 became simply the #3, with the last overlay pens being numbered #403 even though equipped with a #2 nib.
Note that an entirely different numbering system was adopted in the 1940s for British-made Watermans, and that while US-made pens with overlays intended for export usually had a barrel-end imprint with no digits in the hundreds or thousands place, such designations did appear in catalog listings. In a 1912-dated French catalog in our possession, solid 18K gold overlays are indicated by a 7 in the hundreds place; silver, by an 8; and gold filled (doublé or) by a 9.