National and Elgin National

The original name of the Elgin company, in 1867 was the "National Watch Company," as established in the city of Elgin, Illinois.  But fairly quickly, people began to refer to the products as "watches from Elgin" or "Elgin watches."  So, they changed their name to the "Elgin National Watch Company".

The dials on older Elgin watches, from the first two or three years are marked "National Watch Co" rather than "Elgin National Watch Co" or some other variation including the word Elgin.

Now and then, I am asked if it possible to tell, or is it known, what serial numbers of pocketwatch movements fall before or after this change?

The short answer is no.

There are two problems...  The Elgin data on production years by serial number is based on factory records of when ranges of numbers were used.  But Elgin stockpiled parts.  In fact it seems that individual departments stockpiled parts, dials included.  So the year a watch actually came out of the factory could be years after the date we can look up, when the plates were made.  An older watch may not have gotten a dial until after new dials were made.  Or a slightly newer movement may have gotten a years old dial.

Secondly, since they did this, it is just about certain that during the transition dials marked both ways were used for probably a multi-year window.

It might be assumed that serial numbers and the name on the movement were marked at the same time, and if so there was probably some point at which those dies were swapped.  But it hasn't been tracked.  It would probably be different for each grade.