What are the last four digits of your card for?
If you are referring to a credit card, the last digit (the 16th?) Usually has to do with the cards that have been assigned to the account. If a card is to be replaced, the last digit would be increased by one, for example, if the last digits of a lost / stolen card were 4 4 ​​3 5, then the replacement card for the same account would be 4 4 ​​3 6. This practice may have changed over the years at various institutions.

I know that the first four to six digits are "assigned" to specific banks and that Visa accounts start with "4" and MasterCard accounts start with "5". There was previously a scam that resulted in phone calls to unsuspecting people who had Visa accounts and they were asked if one's Visa account started with a "4". YOU'RE LUCKY!
https://milestoneapply.cards/milestone-gold-mastercard-review/