I had a problem with iDine (now resolved) during the UAL December promotion.

It was explained to me at that time that the "matching" is done during the authorization process at Visa.

When the restaurant electronically sends your account and total bill to Visa for authorization, it flags the account to forward a message to iDine to credit your account. iDine is just one of many such incentive programs that Visa (and other credit cards) acts for as an intermediary. *All credit card numbers would not be sent to iDine!*

If my understanding of the explanation is wrong, someone please chime in!