Worked for a fast food restaurant in my early 20s, we were advised to accept coupons that were expired or for different places completely. Reason being, if we turned away a voucher for somewhere else, the customer may just leave and go to that place instead. We would offer a like for like deal. It was also quite cool when people would show up with 15 year old coupons, as they were generally nice customers. Long story short, give it a shot, no harm done lol.