it's not that important anyway.
Well sure it's important. If it's a 99, fine then it's a 140 chassis.
If it's a S430, then the year is wrong and it's a 2000 S430 220 chassis. Maybe the production date or sales date was in 1999, but it's a 2000 model year? There would be different recommendations to be made for the 2 different chassis, very different cars.