Hi Rüdiger,
My understanding is It was to make it easier for dealers/parts dept to understand what equipment would have been standard on a car.
For example,
2000 Models
Chassis Suffix A had a mechanical steering relay with separate damper,
Suffix B onwards had the combined relay & damper in one.
Suffix A & B had the Dunlop 5" Servo
Suffix C had the 7" Lockheed Servo
So anyone in the dealership who need to know could quickly identify what servo was fitted as standard to an early 2000. The changes were always listed in the Service Newsletters and there were some 'minor' changes between Suffix numbers but in general a change of Suffix letters meant there were several changes throughout the car.
Just to confuse things some diff & gearbox serial numbers missed a suffix letter completely, so when the chassis suffix on a 2000 went from A to B the gearbox didn't because there were no changes to it, however when the chassis number went to Suffix C the gearbox went straight from A to C as they were fitting the later type clutch which meant the release housing was modified.
Regards
Alan
