Not necessarily overclocked at least in the normal use of the term. They may have been individually testing each one to find its maximum speed before it starts throwing errors just like Intel and AMD test their CPUs. Once they have enough chips in the fastest speed bin they can make the new model using them. You wouldn't refer to an i7-3.6GHz as overclocked and an i7-2.9GHz as underclocked if that was the speed on the box when you bought them.