NADA is more relevant on used cars because credit unions value cars based on NADA. Credit unions dominate the used car lending market in Utah, where the three largest lenders are all credit unions.

So dealerships will pull a NADA and know where they can expect to retail out of a car. However I find that dealerships primarily use MMR which is an auction based value as the most accurate because why would they pay any more for your trade in than they would pay to go to auction to get a similar unit for? Any amount they offer over MMR is most likely them over-allowing, which means they are going to pay you over auction value and then strip profit from the new car you are buying to lower your trade value back down near the MMR.

Also as I mentioned above, it depends on where you live. NADA and KBB are used more prevalently in different parts of the country.