Here's my take on the "notches".
I started the restoration on my '70 in the mid '90s. I replaced the entire front clip with factory pieces - there were no notches on the fenders. I didn't "add" them, didn't even know as there was no interactive information source at that time.
I have been to Stuttgart many times and been on various tours of the factory. I was on one tour that included the stamping area for large body parts. I was surprised that they only have one die for each part (they cost in six figures for each die). I think what may have happened is that as the die wore down, the "notches" became less and less apparent, thereby making even factory correct replacement fenders lacking the feature.
Just a guess..
Rick