The problem with both NADA and KBB is that they pull their data from two sources, dealers and the very, very limited number of "reported" sales each year.
The data is to some extent worthless, and in the car game is heavily massaged by dealer reporting to ensure they can buy used vehciles for what they consider
to be a good price.
That said, NADA on line provides the values below for a '92 GSPD
KBB on-line says:
Excellent Condition $5,385