The "date problem" arises from mistakenly comparing an overseas industrial assembly line with a small Washington luthiery stepping up to production.
Here's my educated guess. The Wikipedia article says in the early days (~1992) Tacoma Guitars "produced about 100 guitars a month for another guitar brand," so we have a rough guess at their maximal production capacity (I'd say 200 units absolute max).
They released their distinctive Chief & Papoose models about February 1997 at the winter NAMM. That means these were likely still in final development late 1996.
Jim Smith said Tacoma built a few Washburns: D-43 (2nd version, 1994-1997), D-46 (1996), D-47, D-48 (1996), R-310 (1996-1998). With so much on the table, & their own brand starting to get commercial traction, Tacoma likely wasn't interested in being "Washburn USA" for acoustics. In 1996, they declined the contracts for D-size guitars, but agreed to build out the initial orders.
That's probably why some "1996 only" guitars would be stamped with a 1997 serial number. (Only a guess, but I think that's also why Smith says the D-43 went into 1997.)