some clarification :

WhiteAmex : Centurion card numbers look like 37xx-88xxxx-xxxxx , but this is also true for older Platinum cards (as Plat used to be the elite product...).
Departures.com needs an update ...

deelmakur: the 1st card (main card) has always x100x as the last digit sequence. "100" has no other meaning than "first issued card for the main cardholder".

MarshKing: the "99" rule is still correct in some european countries : 37xx-99xxxx-xxxxx. In the last years, Amex introduced many new products in the US, issued millions of new cards (blue, co-branded, etc.) and had to define some other "aa+bb" field combinations. There are also differences between Corporate card accounts for large corporations (with more than 99 supplementary cards) and Small Business accounts. Thanks for the info.

GK: the printed 4 digit number (the card series Nr.) is the same for many thousands of raw cards of the same type. If you loose a Centurion, the probability is high you'll get the same number for many monthes...