is that each of those 10 chips shown came from a completely different set of 7 chips (ie 70 chips altogether).

Had the $5's been 'odd chips' then I would not have bothered.

Now Im going to add something more. I have here, almost all the manufacturers records for these chips, including quantitites made. When I get round to it I will publish them. Some of the chips only had 100 made (which is why no-one can find them), others had 3000 made. Its important to differeniate - we have a price range of $6 to $70 a chip on this series.

"My personal feeling is that these minute variations don't exhibit a desire of the manufacturer to produce a "different" chip. They are generally the result of some slight changes (some likely unintentional) in the manufacturing process."
Its actually a combination of both your comments. When my article is updated (and there is a lot more to add that I have not posted here) it will become clearer.