MMR on the three-year-old index has fallen three months running. Down 1.3% in May, 1.9% in June, 2.8% in July.
Note the shape. Not three flat declines. Each one bigger than the last.
Why this index and not the headline
The three-year-old book is the middle of most used departments. Off-lease age, still under or near a factory warranty, the price band where the volume lives. When people quote the overall index they are averaging that together with everything from late-model to fifteen-year-old iron, and the average hides what is happening to the cars you actually stock.
A store whose used mix sits in that band has been watching its own inventory reprice against it for a quarter, whether or not the headline number said so.
The headline index is an average. Your lot is not.
The part that follows
Accelerating declines in the three-year-old book and a heavy off-lease ramp through the back half of the year are the same story arriving twice. More supply landing into softening values is how a dealer ends up long on exactly the units that are falling fastest.