This is the only 66 -67 I have
I’m fairly certain that here the third digit is not part of the sequential numbering, but rather indicates something else - possibly a production line.Then in 1966, we get the Asian Games version, all from August 1966, or at least all starting with "68", in two or maybe three major number groupings. First we see the 14193 through at least 15662 group, which looks pretty well distributed in that range. Then a huge jump to 80268 through 80987. Then another sizable jump to 86261 from there steadily marching to 88140
View attachment 499298
These are uncommon watches, so data points are thin, but with the 22 examples here, they seem to be pretty clearly grouped. It took Seiko 10 months to manufacture around 100,000 world timers in 1964. Could they have really made 88,000 in a single month in 1966? It doesn't seem likely. Perhaps the third digit has another meaning, or maybe Seiko was sharing numbering across models this year/month, or maybe they just skipped large sequences... ?