old coupon cannot be deleted ?

Hi

We have a long list of previous coupon , it looks really mass on the page ui, can just want to delete all the old coupon, but when I try to delete them. I got this message:

"This coupon is referenced by an order and therefore cannot be deleted. Disable it instead."

and the problem is there is no links showing which previous node has using one of these coupon.

SO, How can we delete all those old coupon, there is no way to showing them on the site permanently, but from the module saying now , seems we can never delete them, because we have hundreds node associating with them.

Please advise. thank you.