Gary;
I think it could be said that nothing at Smith & Wesson is written in "Stone" more like maybe "wet cement" that finally hardened and became the Records. Serial Numbers weren't shipped in Numerical Sequence, engineering and design changes were incorporated as the old parts were used up and things like Dash Numbers were added in something less that an exacting manner; sometimes. The Factory was in the business of building guns; not keeping meticulous Records for us Collectors; especially during times like when the 1917s were in production.
Also, since these 1917s were built as "piece work" not every employee has access to the "Latest and Greatest" parts and simply used up those he had in stock at the time of the building. I understand that these "piece workers" were simply issued a fairly large number of parts and would be re-supplied when they ran 'low' not just when they ran 'out' completely. Thus, they might have parts that were several years old but were still brand new! New Old Stock.
I was in the Depot in Panama while I was in the Army and was assigned to a work bench that included 'parts bins' for many different firearms. Basically, everything that was still in the "Inventory" or 'might' still be around. Those 'bins' included some original 1911(not A1) parts, Geasegun parts and old vintage "N" Frame parts. Of course, many of these parts bins were covered with years of dust because nobody had gotten into them for years, but it just wasn't the Army Way to spend time sorting out and tossing parts that might "someday" be needed.
MAK