I'll measure the stamps a little later . Here is a link to the Japanese site . It covers all eras . I haven't attempted to read or translate it yet . http://www.maroon.dti.ne.jp/miura/html/equipments/zildjian/azildjiansp.html
Ah. I've seen this site before. And like you I wish I could read it all. It makes me feel so monolingual. I've put some things through google translate in the past. I remember I found it inconsistent with all the traditional English sources (which are themselves inconsistent with one another).
Just measured the stamps and they are both 30/31mm by 26mm ( widest at ZILDJIAN ). According to the Japanese site this means they are from the mid 70's to 1981 cymbals ( size and 3 dots match ) . Also , according to this site the early / mid 60's stamps were 40cm tall !? This Japanese site looks to be extremely informative .but unsure of its accuracy . Normally Japanese are very anal with regards to information on vintage drums so I tend to trust it . Wish I could read it all .
I'll have to go through their specific mid 70s to 81 example(s) again. But as a quick point, make sure you haven't overlooked a ZILDJIAN & CO versus a ZILDJIAN & Co. The CO makes it much later, although I don't know how much later. An 80s stamp as best we know anyway:
[img]http://black.net.nz/cym2014/Z-80s-CO.jpg[/img]
Note this one only has one dot rather than three, but that's due to the other two being very faint in this stamping, as far as I can tell.
The 30/31mm fits perfectly with Bill Hartrick's original timeline for early 60s. 40mm for early to mid 60s means you would have to revise Bill's work and claim he got the dates for the early 60s and the late 60s reversed. He has 38 mm as later 60s, not early. Note that people might use 40 mm for reporting purposes no matter how anal they are -- just because of the well documented tendency to round/truncate to "nice whole numbers". That's why I only report it as 38 mm, where in fact the conversion from his original 1.5" (which is itself approximate) is 38.1 Unless...the Japanese site 40mm is a true distinct size (different from the 38mm) and hitherto unknown to Bill Hartrick (and others in the West). In which case the timeline from the 1960s onwards to the 1980s needs revision. No I believe it does need revision, but not just because of this one uncertainty. Now matter which way you turn there are troubles of interpretation.
The two other sites commonly used (because Google finds them) are
http://robscott.net/cymbals/
and
http://www.hidehitters.com/cymbals/Zildjianstamps/timeline.html
and robscott defers to hidehitters for A Zildjian. Both show obvious inaccuracies, particularly the hidehitters site. The problems may have as much to do with mistakes in formatting and headers as much as actual dates. I've actually considered cloning the HTML and correcting it, and then sending the corrected version back to him. For an example consider the heading: Big Stamp 1953-1963. It should be called a Large Stamp according to Bill's publication which has naming priority (in Science whoever publishes first wins rights to name things). There are three types (missing from hidehitters) and although the heading says it goes to 1963 this is inconsistent with the content which follows, and the next section on the 50s stamp, and of course with all of Bill's work. Hidehitters and robscott also fail to give heights which are sometimes the most important attribute for identification. Those sites are in need of upgrading (and giving credit to Bill).
In no case do any of these sites: hidehitter, robscott, japanese one, nor Bill's original article give sample sizes and how the cymbals were dated so we don't really know the strength of evidence for any of the timeline dates. If you read his original article carefully you will see Bill understands the different kinds of evidence you might use and gives the appropriate cautions on deriving accurate single year dates. But that caution got lost when timelines started being used and placed on the web.
So we've opened up a riddle wrapped up in an enigma inside a mystery.