I know that at my commisary we can not use them once they are expired. I tried twice with two different cashiers and they both said no because they are actual checks that get deposited in the bank. Which actually worked out for me because then I priced Enfamil formula on the Dutch economy for my baby and it was half the price compared to the american version even with the exchange rate! Unfortunatly diapers are double on the dutch side.
Hope this helps!