Most people think of credit card numbers as what is used to recognize credit cards. This is true, however, banks change the credit card numbers all the time without actually changing the other aspects of the account. When you get a new credit card to replace your old one, the account remains the same.

This is achieved using what is called PAR (Permanent Account Reference). PAR is a 29 digit unique identifier that is assigned to a credit card account you have with a bank. You might never see this number but it is available to merchants and wallets who store your credit card info. When a merchant or wallet provider has a credit card stored, it might also store the PAR to make sure they can correctly identify duplicate cards in future.

PAR is no a sensitive number in a sense no one can do financial transactions using it but people might be able to use PARs to figure out which cards ultimately belong to the same user and hence there is a good reason for banks to not reveal it to every except those who need to know it.

The advantages of PAR is better user experience, better risk analysis and improve security of accounts.

You can read more about it here. https://developer.mastercard.com/payment-account-reference-inquiry/documentation/