It was introduced with the Mac Pro's, beginning of August. You can check the serial number of an ACD by filling it in at Apple's website somewhere under support. Then it gives back the specs of that display/product. There are a couple of threads about this in the Mac periphals section.
I also bought one from an Apple Store (not really an Apple Store, because we don't have Apple Stores from Apple, but they are in private hands and can call themselves Apple Stores), but they gave me an old one. So I returned it.