Part numbers for MB vehicles used to have 10 digits, e.g. 113 985 01 02, of which the first three describe the vehicle or engine model, the next three the group (e.g. injection, electric etc.), the next two the version (from 00 to 99) and the last two the subgroup within the group. While the engineers designed the part or car, a special standards department, Normenabteilung, issued all the part numbers so that no two engineers could use the same number.
This department also looked for free numbers or a group of free numbers when R&D told them that they wanted to build a new series of models. There was no rule for a link of these internal numbers to others in the system, besides that the first digit had to be
1 or 2 for passenger cars and passenger car gas engines
3and 4 for trucks, buses and their engines
5 for large diesel engines (e.g. boats)
6 for diesel engines
7 for gas turbines
8 for military engines (e.g. for tanks)
With the advent of the 201 it looked like there would be some order (201 and up C-Class, 210 and up E-Class, 220 and up S-Class, 230 and up SL-Class), but with the CL and CLK models inbetween this order is already crowded that it can't last very long.
Klaus
1969 280 SL
