I am sure a lot of you have run into the problem that the in-ad coupon says "manufacturer's coupon" on it. I have had cashiers reject the 2nd coupon because they say I can't use 2 manufacturer's coupons. The truth is, the in-ad coupon is a store coupon, which can be combined with a manufacturer's coupon.
Saving this ad is a little insurance policy for yourself. Whether or not it will work depends on your store, but it sure as heck should improve your case. The proof is in the pudding! :)