I have never heard (seen) this discussed. Was it Metal Leve who supplied the pistons to VW in the MK. II's.
I just bought a new set for a "no-frills" N/A rebuild and they have the appearance of the originals......with somewhat of a "Homer Simpson" look about them. I went this route because Prothe is currently out of the Right Way Industrials (which are working very nicely for me in an N/A) in the 0.5 mm bore size.
And, before you ask....I've got a brand new set of KS sitting in their box for the ECO when it's time comes. Whenever I can get to it. The engine currently undergoing "the knife" just isn't as critical. They are, however, getting expensive German rings.