1 vote for a matched set from 1980. Very pretty!
I've been working on this problem of when serial numbers began. Not as long as I've been working on sale prices (meaning I didn't record serial numbers really carefully until a couple of years back). In fact, I didn't know it was going to be such a tricky problem until I got a bit more interested in it. And I don't have all the answers. I don't know if we ever will...
Until somebody shows up with the original purchase receipt for those which proves 1970 rather than 1980 I'd say the balance of probability lies with those being 1980. I would love for you to come up with the purchase receipt because that would be an important piece of information.
Paiste have said that the initial digit as year is only "approximate". I presume that's because the serial number didn't get changed at midnight on December 31st of each year. Similarly the changes between the black labels and the blue labels didn't happen on January 1st 1980. Inconvenient, but things just don't change precisely on the year or decade boundary. That fan page timeline you found suffers from the classic problem of artificially lining everything up with decade and year boundaries. The Pasite-only one is more complex and more realistic based on my own research. Changes start part way through years and part way through decades. Inconvenient, but there it is.
If you go to the 602 series overview in the wiki
http://www.paiste-only.com/paistewiki/index.php?title=Formula_602
there is a slightly different presentation of the info. In this overview serial numbers start in 1973 (Black label period 1973-1980) followed by the Blue label period (1981-1989). That is also a bit oversimplified as well. But if it were taken as a working hypothesis then there shouldn't be any Blue label 602s which start with 0, and there shouldn't be any Black labels which start with 2 or 1.
What I've been trying to do is find the serial numbers of Blue labels and Black labels and plot how many of each start with which digit. I need to do a database retrieval and refresh my memory on what I've got so far. If you plot all the serial numbers for Blue and Black, once you have enough the pattern should start to emerge.
It ought to be easy to check on the distribution of first digits...but I know that's "famous last words" since I expected to be able to do the same thing with picking up the differences between heavy/medium/light in other 602s which had lost their red ink designations. Data driven work is tricky and you need to wait until you accumulate a large sample. I'm reasonably happy with the weights for the 20" ride (as in one link in my signature) but data driven classifications aren't really strong evidence.
In my database I do have a number of 602s from 1972 which do not have serial numbers. But that doesn't prove there aren't any. Just that some don't. *sigh*
There is also a thread or two on Paiste-Only (the forum not the wiki) where those who have been at this game longer than I have talk about subtle distinctions in the details of the 602 stamp itself. I'll have to recheck those to see if that work adds more clarity. I remember that the pre serial to black label period doesn't happen all at once. There are intermediate steps like the model designation (Medium Hi-Hat Top) going to black ink rather than red. But I can't remember the proposed order off the top of my head. What I do know is that the black ink Paiste Formula 602 appears on cymbals before the serial numbers do. I've got a pre serial 20" flat like that which says "Pat. Pending" (which also helps date it -- but that's another study).
The paiste-only forum threads I've got bookmarked are:
http://www.paiste-only.com/phpBB2/viewtopic.php?f=1&t=4668
http://www.paiste-only.com/phpBB2/viewtopic.php?f=1&t=3600 (less relevant to this question)
But you've got some reading ahead of you because that first one is unstructured. The second one may mr may not yield info on this issue. I've also got half a dozen bookmarks into Cymbalholic but that's offline for some time so I can't follow those up. Alas.
Also, I don't know if the weights of hats tend to change over time in a way which would help clarify (or just add more data but no enlightenment). I've got lots of weights but I've never really done an analysis on them. Have you got weights for yours?
Back later...