50's A's with the BIG hollow letter ZILDJIAN stamped into the metal already had 3 dots by then,so,your's could be older or late 70's,when they took the dots out again.
The hollow logo you're speaking of is 50's, as is the one that this gentlemen has. I have both types of logos on two different cymbals, as well as a 70's thin stamp,
This cymbal is definitely 50's, my only question is did the hollow block stamp come out before or after this stamp.