[SIZE="4"]The "60's stamp" didn't necessarily end in 1970. It's called that because it was used longer in the 60's. I just sold a set of brilliant Zildjians, of which the bottom had the same "60's stamp," yet Zildjian didn't start making a brilliant line until the early 70's.[/SIZE]
Yes, the "late 50s stamp" didn't end at the last day of 1959. It may well have lasted though the early 1960s. We just don't have a way to be that accurate.
The "60s stamp" (both of them) didn't end at the last day of 1969. They may well have lasted through the early 1970s. We just don't have a way to be that accurate.
We don't have a solid date for the hollow ink Zildjian logo on the bottom either. Could be 1973, could be 1978 (sources vary) and it could be different. There are hollow ink Zildjian logos on "60s stamp" cymbals. We just don't have a way to be that accurate.
We have a first year in which Brilliant finish on Avedis Zildjians was advertised (June 1971). But that doesn't tell us how much earlier it was available, or if there is an earlier ad we haven't seen yet. From time to time brilliant finish A. Zildjian cymbals come up which look to be from the 1950s, including some Trans Stamps. But we have no way to know if these represent buffing up after they left the factory, or if they were done at the factory on special request.
The only reason I use the term "late 50s" or "60s" or "70s" is a shorthand, and I try to indicate on my site that these terms should always be understood as having several years of uncertainty involved. But it gets clumsy to write out the uncertainty every time something gets a mention:
That appears to be a "1960s" stamp which may really date from just before 1960 through to the early 70s and overlaps with the hollow ink Zildjian logo on the bottom which is usually thought to be just "70s".
I've started sprinkling ±2 or ±3 around the place, but even that doesn't help too much when the likely years aren't symmetrical about the year given. And I'm not going for "1960 in the range 1960-1 to 1960+12 with p<0.01" if I can help it. :D