...if you take off the bracelet you will find the model number between the "12" lugs and the serial number between the "6" lugs, both of which would be helpful to know. As would pictures, of course. Could be the watch has a 6240 back but is a 6239 and that's what was noted on the paperwork.
Here is an early one for reference, albeit with DAYTONA and without "Oyster" (1st gen dial):
Good luck & hopefully you can show us some pix of this interesting watch.