A check digit is a semi-random ISO standard number 0-9 or X (10). What happens is you change the letters for numbers, add everything up then divide by 11. The check digit is the remainder. It's a computer verifiable identifier. If you had 1GTCW80H9DD500592, but the car was an 84, it'd read 1 number more than that or 1GTCW80H**XE**D500592, the E being 84 so changing the remainder of 9 to 10 (X).

So if absolutely positive about all letters and numbers except the plant letter, it has to be a D as B, R, K, Z, 1 plants add upto a different remainder, usually 4 or 5 for the check digit. With a 9, the only plant that fits (all other vin letters correct) is D with check digit 9.

So if absolutely positive the plant is B or R, and check digit is 9, and it's D for 83, then one of the other numbers/letters is incorrect. That's the purpose of the check digit, an identifier, all the others have to add up and divide by 11 for it to be correct. It's not different check digits for different plants, it's different check digits according to the total of all the letters/numbers.

According to the DOT vin check digit calculator, there's only 2 possible vins that match up.

1GTCW80H9BR500592 which makes the car an 81 not an 83, or 1GTCW80H9DD500592 for an 83