AWD numbers are assigned to long term negotiated contracts between corporate accounts and Avis. Coupon codes are relatively short term (months) promotional perks assigned to various promotions. Coupon codes are generally subject to blackout dates and other restrictions, and have somewhat limited value to the frequent business traveler in my opinion. And yes, I would guess that most people are aware that both programs can be applied to a single reservation since you are allowed to enter both numbers on any reservation. It's not as complex as you would imply it to be.