Mike,
First you get a Data Card from MB Classic Center. The Data Card is specific to a single car produced.
Then, quite simply, then if the numbers on that Data Card, match the numbers on your car .... then you have numbers matching the data card .... which means you have the same components (engine, transmission, frame, front hood, convertible top cover .......) that the car was originally built with. That is, unless someone did something like faking the numbers.
Having matching numbers doesn't guarantee anything, but having numbers that don't match does guarantee that someone has changed that component or part of the car since it left the factory. Of course since it has been a half a century since our cars were built, some people (ME) think it is cool to have the same metal all together, all those years without someone switching something out.
That is it.
If you look in the Tech Manual of this site, there is a lot of information explaining exactly what is on the Data Cards. They changed over the years and we even have all of the details of the changes in the Tech Manual.
I have seen that you have questioned this before.
If you still don't get it, speak up and we will try to explain more.
Good luck,
Mark