As I understand it, whatever car class reservation you make National was required to give at least that car class. If they were out of that class, they should give you a higher class for free. I believe this was regardless of Aisle or Counter service.
The Emerald Aisle gave you an bonus - pay for just an intermediate, and have the option to get take any car class that was in the aisle. Presumably if the aisle was completely empty, you'd go to the counter, and they'd give you the intermediate you booked.
Many people legally took advantage of this, and booked a higher class, either standard or full, for often the same or a few dollars more than the intermediate aisle rate. We still had the option to get any car class in the Emerald Aisle, but if it was empty, we could go to the counter, and request what we reserved (say full size).
It sounds like this is now gone. If you want to guarantee anything larger than an intermediate, you need to pay for it. If you want to gamble that you can get a fullsize or SUV for the intermediate rate, you need to give up right (via a reservation) to anything larger than an intermediate. Do I have this correct?
If so, what is to stop me from making 2 reservations, one for Aisle at the intermediate rate, and another for Counter for say a fullsize. When I get to the Aisle, if a fullsize car is available, I take it (at the intermediate rate), and cancel the fullsize reservation. If I don't like what I see in the aisle, I go to the counter, get the fullsize, and cancel the Aisle reservation.
Since there's currently no penalty (at least for most places) in cancelling a reservation, this would seem to be the way to go. National loses out because of these phantom bookings.
Jeff