Wow, yeah. Mine seemed to fall in the window of Alps'
actual speculated timeline when considering when pine Alps stopped appearing in their catalog. The boards I have that had pine were from 1990 and 1991, while the bamboo boards were from 1996 and 1997 (the only one made in Mexico was the 97 model; perhaps 1996 was the last year of US production?).
The 1997 pine Docutech you have is very strange, but I can imagine it could have been serviced and had the entire PCB swapped out for an older PCB that was ready to go in the early 90s. I can't imagine they went through the pain and labor of swapping every switch out and putting in pines. I'd think that you'd more likely see a mix if they were replacing switches individually.
On the other hand, it could be possible that they made a late batch with pine switches that were still in stock.
Can you check the PCB of the 1997 pine board? Both of my pine boards had PCBs like this:
While the later boards from 96 and 97 had different pcbs:
The chips are also different. On the earlier model, the controller was a NEC chip while the later models had Xerox chips
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Also the connectors on the older 90 and 91 boards had 89 in the numbers stamped on them:
The 96 had "95" stamped on it:
and the 97 had "97" stamped on it.
Also note the subtle differences here. The later connectors have a "frame" around those numbers in the middle while the older ones don't.
So check that to see if maybe you've got old components or not. The IC chips themselves should have stamps that tell you the date as well.
Lastly, here are PCB revision numbers:
For the early Docutechs
For the late Docutechs