I have what I believe to be a 50-60's 20" Avedis Zildjian ride cymbal. According to the web research I was able to do, this one rolled off the assembly line early in the production run because the "stamp" is barely visible, indicating that the machine used to brand the cymbals was not yet accurately calibrated for the remainder of the run.

Small keyhole has been ground to prevent further damage. Nice patina. Sounds beautiful! Photos upon request.

Similar items on vintage sites selling for $200-$400. Make me an offer, please.