In reply to (No subject) by FifthAvenueRes…
The above 10AA has no date symbol, and is housed in a case with a tentative production date. It also has a movement serial number. The watch record has been dated based on first digit of case serial number, but we see many, if not most of these 1919-1923 cases having serial numbers beginning with a 1. This date/period is partially backed up by a couple tentative ads for the 155 model (I think 1922 ads). Based on the movement signature of Bulova Watch Co. this movement is, in my opinion, 1923 at the earliest- more likely 1924.
I don't know if this helps but I have an older case filled with stems(Bulove genuine standardized stems)and on the cover there's a interchangeabilty guide.One line lists the 9AN as being interchangeable with:9AT-10A-10AA-10AB-10AE-10AEcs-10AM-10AN-10ANcs-10AR-10AX-10AXcs movements.I don't have a 9AN stem or else I would offer it to you for free.Also I don't know if the stems listed are all interchangeable.Hope this helps.