The fact that they were put in is proven. Why they were put in is subject to conjecture and opinion. There are different length versions, which are original or not, I don't know. I've seen some really long ones.
I do know that it is impossible to prove exactly what is original or not on all cars; specifically if you are the nth owner and 40 or more years have passed since it was made. How do you know with absolute certainty (unless you are the original owner) that no work was done on the car? Can you prove no work was done on a fender bender that happened in 1965, 5 owners ago? Most of us would hardly believe what the cutting torch revealed when my car was worked on during the restoration...
Today, those notches are simply a metric that indicates that whoever has done work on the car has at least a greater than average understanding of the car, and at least a more than passing interest in a bit of accuracy. They are so small as to be nearly invisible unless you go search them out.
Recently I saw a 230SL owned by someone owning a local collision shop. Not a member here, not a member of the MBCA either. The car looked quite nice from a distance--new paint and all, generally a good looker. But details? UGH! No notches, wrong wheels, man--if it were posted here you all would pick it apart like vultures on a deer carcass! Clearly the owner, and his own body men, treated it like any other car. Sure was shiny and pretty, but a tremendous lack of correct details. A sin of omission, not commission.
We like to think of our cars as special and one of the ways we do this is generally pay attention to little details like these notches.
Michael Salemi
1969 280SL
Signal Red 568G w/Black Leather (Restored)
President, International Stars Section
Mercedes-Benz Club of America