I think you don't have to feel sorry.
In fact, I initiated this deal yesterday and I clearly mentioned the possible confusion. So a faithful reader (who reads most of the threads) would have been ready for it.
It is no surprise because the spec in CompUsa website indicates that it is a 3520.
Insteading of feeding Mag Dog the right product = 3500, NEC just decided to pack 3520 instead. That's my guess. In most circumstances, it's a benifit to the sellers and customers because it's a new model. But the comparison between 3500 vs 3520 is so subtle... so it may be an exception.