The case serial number does not indicate when the watch movement was produced which increases the possibility that the movement is older than the watch case.
When examing watches at an AD or watch mart, do not be surprised if a bracelet is a few years older than the watch case.
The letters represent the year code, and the numbers signify the month.
A clasp code of OP9 indicates the clasp/bracelet was manufactured in 2006, and the number indicates the month of September.
Rolex frequently uses numbers and letters to identify model year, model number, bracelet type, as well as other production variables.
Although not verified by Rolex, these numbers are fairly prevalent on the Internet.
The serial ranges listed will provide an indication regarding the date of manufacture.