People generally call it the 60's stamp, however that is not definitive. Zildjian will tell you to add or subtract 10 years for a reason. I had a thin one with that stamp, but it also had the hollow logo Zildjian ink stamp, which officially placed it's manufacture between 1978 to 1981. If there is NO ink, there is no way to tell if it ever had the hollow logo or not.Yes, it could be early 80's.
Yes and no..
The finish is different...lathing look/feel..
From the pic provided...i zoomed in 200%...
60s....!