Hi Paul,
It should be possible to fix the date/time problem by
dumping
the DECmate's ROM and disassembling the code.
https://en.wikipedia.org/wiki/DECmate#External_links includes
...
DECmate II ROM contents, decoded and disassembled by Charles J. Lasner
https://web.archive.org/web/20051218090251/http://anachronda.homeunix.com:8…
Hope that's a match.
--
Cheers, Ralph.