I am the "forgotten FT'er" ... I'm still alive

Thanks jgsx for remembering me this (very) old post about the card structure.

In this classic scheme, the first six digits used to describe the exact card type (Green / Gold / Platinum / Corporate ...) and issuing country (base currency).

The US uses many "issuing country" codes for charge cards, the rest of the world uses one code for each country , credit cards have a different one.

This system reached his limits in the 90's already due to the shortage of available numbers. Amex started to upgrade accounts without changing the base card number : The new card was issued updating only the card sequence number (4th digit from right) leading to a new computed check digit (last digit).

The "88" as 5th and 6th digits 37xx-88xxxx-xxxxx indicating the premium personal charge card (Platinum card in the early 90's, then Centurion card) seems not to be true anymore for newer Centurion accounts.

All remaining fileds (the base account number, the 1 digit sequence number, the 2 digits for main and supplementary cards, the check digit using the Luhn-10 algorithm) are still the same.