I agree with Bamaman1, I think that NADA prices are inaccurate because there is no nationwide source of data for them to access. Their used prices seem to be depreciated numbers based off MSRPs for new units. And very few units are sold at MSRP pricing. According to NADA, my almost 4 yr old unit is worth more at Average Retail than I paid for it brand new.
And definitely, costs on new units varies between dealers based on volume discounts and special incentives. So between that and varying selling discounts off MSRP, NADA has no idea what actual new unit pricing is and therefore, their used prices are overinflated.