I often mix and match contract id and coupon code, but it's not always easy to determine which of them is for which part of the promo.

Take this Northwest promo for example,

Rent a ...... receive Triple Miles plus a double upgrade with National.
...
Please request Contract ID 5004067 and Coupon ID NU5.

Normally, I would say Coupon gives one the upgrade and fixed $ off
while contract id gives the bonus miles, % $ off, complimentary LDW, etc.

Does this sound right? Also, is there any known exception on mix and match contract id and coupon code?