I'm so confused by the acronyms.

EA = Emerald Aisle? or Executive Aisle? What about ES?

It would seem that Ea = Emerald, Es = Executive.

I dont have executive status with National, I just signed up for the free Emerald Club... so to get access to 'choose my own car' I'd need to reserve a midsize and choose from the EA not ES aisle... is this correct?