If you do a change of address with the post office, they normally send that coupon. Just pick and old address of yours and say your moving to your current address. It's not wrong, it's just delayed, and you get the coupons when you can actually use them.
Those coupons are only valid with use of the HD credit card, and I was told by a customer service rep in-store that you can get the deal anytime you like if you go to the store to place the order and ask for the 15% off coupon to be applied.