Will,
We're currently basing the production dates of these early Watches with Movements absent of a published Datecode on their Case serial numbers only, which at this time is unproven. It still remains that the Case was manufactured in 1921 by American Standard as suggested by the trend seen 1924 - 1949.
scenerios are:
A Movement Cased in 1922 '23 +/-, which is not out of the question.
The method of dating the pre 1924 Cases is incorrect.
or
The new theory observed on the Movement hallmarks is flawed.
We have yet to fully determine what is actually going on here and this example would indicate further observation of the Case serial numbers and Movement hallmarks are necessary before making any firm conclusions, though the Bulova Watch Co hallmark showing on the Movement does suggest 1923.