It's actually the compliance date rather than the build date, if I remember correctly a car couldn't be compliant until complete, so I guess the Compliance Plate would've been one of the last things to go on, as opposed to the Body Plate which was one of the first to be fitted (hence why it's painted).
Is yours the integrated air con with the evaporator in the engine bay, or the "knee freezer" under-dash type? The latter were all dealer-fitment as far as I know, so couldn't have delayed production.
We're only talking about 160-odd vehicles and perhaps a matter of days either side of the Christmas / New Years break, and remember that sedans were included in that chassis number count as well as all the different luxury levels.
Also, a Hatch was a completely new thing back then, with yours being one of the first ever made there could easily have been some issues with the way it went together, or parts supply, or something?
I wouldn't stress about it too much anyway.