I would use the expiration date on coupons as a guide, I would except a expired coupon as long as its "within reason" of the expiration date. If a customer isn't "normal", meaning they have all expired coupons or are "extreme couponing" I wouldn't except them, since these customers are going against "our goodwill". If a customer has 10 coupons and 1/2 is expired by a day/week, don't even worry about it. If a customers has 10 expired coupons on their mega event items......sorry your just playing promotions.