I have a Louisville, Kentucky, watch sold in the 1830s. It has the serial number 3. This number was of significance to the retailer, not the maker. I have many other Anglo-American fusees with much higher serial numbers, in the tens of thousands. Those sorts of numbers were not of significance to the retailer. In general, who decided what number was engraved on the plates and why? Any chance it was the engraver? It seems to me one of the last steps in the manufacture of a watch movement was to have the plates engraved. The engraver may have been only loosely connected to the watch industry as he and/or his shop would have engraved any work that came in, whether a watch, a scientific instrument, or jewelry. If he consecutively engraved whatever entered his shop, then this might (partially?) explain the apparently weak correlation between serial number and assay year that we observe today.