Sheaffer Special

At an auction in Grinnell, Ia a few years ago I purchased a small lot of pocket watches. When examining further I discovered 2 movements which are Sheaffer Special pocket watch movements one O size serial number 2331508 and one 12 size #2283108. On the back engraved on both is "Sheaffer Special, Mount Pleasant and Bloomfield, Iowa. Also the dial says Sheaffer Special. Both are Lever set which dates probably pre 1910. After researching I have found that Sheaffer of Sheaffer Pen actually started as jewelers in these 2 cities. Some suggest that they bought Hamilton watches and private labeled them but when running serial #'s this is not the case. Ran # thru Elgin, Hamilton, Waltham and Illinois Databases. No matches. Could not find any factory markings. Could it be Hampden? Since this was in the area that their watch maker business was located I doubt they are fakes. Can you help me find out what brand they are? Did they make them? The O size is pictured.

Thanks,
Clay

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Referring page: http://www.collectorsweekly.com/search.php?q=sheaffer+pocket+watch