No expiration date on mine either. I wonder if it's because I have a Hilton credit card that gives gold status. I should have gold status from stays last year but I already had it from the credit card, so I never got any acknowledgement or expiration date. I have the Citi card which is going away, so maybe they will add an expiration date then. I should make gold again this year, so the gold status from the card is irrelevant.