For what it's worth, my blacked-out-black Turbo T has a build date of 10/86 and last 6 digits of 414549, difference of 50739 from last VIN.
Right, only 20,193 grand national packages were built. But altogether the same drivetrain number of vehicles is the sum of all the turbo-t's and gn's and the like with the turbo 6.