1. If the user handles a debit card, the user generates a card number when handling the card. If he handles a savings card at the same time, there may be a corresponding savings card number, so that the user will mistakenly think that a bank card has two accounts, but it is actually two cards and two card numbers.
2. It may be that you have applied for a dual-currency card, and the dual-currency card will have two households per card;
3. After the user handles the credit card, he handles a secondary card, so there may be two card numbers, because the secondary card exists by relying on the main credit card.