The problem with used car "values" is that KBB is owned by AutoTrader (so they have incentive to inflate the value of vehicles since they facilitate a big chunk of the used market) and NADA is owned by JD Power (who also has incentive to inflate the value of their vehicles so they can sell advertising to car companies for more).

So the prices in the price guides have been massaged and don't really reflect the real market value of things (or worse, they have enough power to distort the market value).