I managed to find a bit more info on the mystery donna... just to let you guys know. Basically the bag was the same as the old style donna, but it had different zips, and the interior tag said 'alexander wang new york' rather than just 'alexander wang'. the ebay listing said she'd bought the bag from Barneys, for $825.
The only picture I could find on Google of a Donna with the same zips, was on a girls blog posted in 2009, and it credited the image as Barneys.
I then found this:
http://forums.thefashionspot.com/f56/alexander-wang-handbags-77145.html
in which one girl in 2009 spoke about the first batch of donnas having the 'alexander wang new york' tag, and being priced $825... so finally the bits of the puzzle fit together and now i'm happy it's authentic so i purchased

just thought i'd let you know in case one of these 1st edition donnas should crop up again
x