The 701 and 702 are easy to tell apart - the 701 are only available in white, and the 702 are that blue/black color with the removable cord. I don't know if the 702s are serialized, but the 701s are - lower is older (mine was in the low 30,000s, and I bought them in mid-2008, they came out in 2006). The gentleman who bought them had no issues with them either - wish he posted more, he owns like 3-4 pairs of K701 and could probably illuminate this discussion a lot better than most of us.
I just remember hearing something about AKG shifting their factory to China in the last year or two, to combat rising costs, and I would suspect that means new tooling and new assembly lines, that could lead to some variation in the finished product. That's why I bought it up. Could be wrong though.
The weirder variation is that I've seen 701s and 702s measured for CSD and they can have different waterfall plots - some have a treble ridge, some don't. I'm not sure what to make of it. Here's an example:
Those are supposed to be "absolutely identical except for the color of the plastic" -
So then the next question is - are we certain that all three colors of the Q701 are even the same?
The whole thing makes me curious as to what I'd get if I walked into a shop and bought a new AKG 700 series today...
Then the guy I met at the Head Fi meet had K701 - they were white!
This is more mysterious than Jimmy Hoffa's disappearance!