I do know that the unit numbers are designated by the license plate on the car as it will have ISP-XXX whatever the three digit trooper number is or was. That year could have even been a centennial plate issue too based on what I found here:
http://www.statetrooperplates.com/isp.htm
I have to wonder if there was something put inside the glove box lid or on the firewall or even behind the gas cap door somewhere.