Can you post a few pics? From what I've read in the past on these they can be hard to date by serial alone since some numbers repeated in different contracts, and dating is easier to estimate by markings, style of font, etc.
You can try sending an email to info@fnherstal.com Include what information you can find on the gun, and perhaps one of your good photos of each side. I've had people tell me that they take a awhile--maybe a couple of weeks, or so--but they've been helpful in the past.
Thanks for the address - I've sent off a message, with a couple of the photos attached, asking for any info available regarding the date of manufacture. I'll let you know if I hear anything.