It does not seem possible that the 680 sold more units than the 7900's throughout the world.
IIRC OcUK where beaten on 7970 pricing by a lot of other e-tailors which limited their sales number and then with the 680 launch OcUK had the most stock and only existing stock globally at some points. So it could be perceived that way if you take OcUK as the only sample of the market.
Even though I did ask in threads about 680's initial launch stock, nothing was confirmed while 7900's we had figures and pyramids.
I can't comment on what happened worldwide, it is entirely possible the 680 sold siginificantly more than 7970, also possible the 7970 sold more
I don't think OCUK were that uncompetitive on launch day as I recall, they were one of the few that had stock, and those that had stock at lower prices quickly went out of stock. Put it this way they were as competitive on 680 as they were on 7970 as I recall.