Cracking The Code

Above are pics of many of the Metro North cars I took this week... was wondering how they numbered these trains since there aren't some 9,000 cars riding the rails. My thought... the first two digits represent the year these cars should have been retired... some 15 - 20 years ago

The pics:

1. 8924
2. 8934
3. 8965
4. 8531
5. 8449
6. 8975
7. 8423
8. 8659