I'm always fascinated to see the date-code spread on these, BTW. The CPUs invariably have 1983-ish date codes, except by the end. For example, Skippy's CP1610A has an 8927 date code (27th week of 1989), while Lathe26's has an 8327 date code on the CPU (27th week of 1983). (Aside: Weird Al would approve of the 27s there.)
You don't really ever see date codes for the middle years. It seems like there's a bunch of NOS (new-old stock) and then suddenly new date codes, at least for the main components. Heck, many of the RAMs have 1982 date codes.
Looking at the chip date codes for the newest chips might give us better insight than the serial numbers. Much of this board's content is from halfway through 1989. The GROM is 8927 also.
This machine was built no sooner than 1989 week 27. At the same time, the GROM and EXEC were socketed like a prototype. We know the next (final?) revision of the STIC1A has datecode 8930 (and the marking "BV2"), so it probably was built before week 30, or at least not much after week 30 once the 1989-week-12 chips got used up.
FWIW, I've seen another 8912 datecode STIC1A with the marking "08E023-4". I wonder if that second marking is a lot code or something. It seems unlikely they'd have two different variants of the STIC1A built in the same week.