Picked up this 16s Interstate Chronometer uncased on the giant auction site some time ago (cheap) and have been meaning to post on this topic ever since. Finally got around to getting the watch running, putting it in a case, and taking pictures.
The Meggers book says on page 388 it is a grade 605 model 7 from a run of 50 in 1915. On page 244, the grade 605 also appears in the discussion of the Interstate Chronometer private label, which the authors describe as having been "sold by Sears, Roebuck & Co. only in 1911." They then list production for the grade 605 model 7 at 300. No date is given, but the book's production date table shows a couple of runs in 1911.
Wondering whether I had bought a legitimate Interstate Chronometer, I began searching for a 1915 Sears Catalog. I found one, which included various Interstate Chronometers, but not one like mine. However, the 1914 catalog listed a 16s, 17j open face version for $14.30 cased, manufacturer of the case unspecified. I will post the catalog page separately.
In any event, it seems clear that Sears sold Interstate Chronometers as late as 1915 and that Illinois presumably continued to produce the watches until that point.
John You have a legit Interstate- They made 2 different models- the early " 175 " and the later " 605 " I have a mate to yours with ser # 2,699,436. I think the " 175's " are more common but both are fairly scarce- I also have a " 605 " Model 6 with ser # 2,582,912 I worked for Sears for a while so I have a liking for these