If its a polar (meaning white dial) the only candidates are 16550 and 16570 (the 1655 was only produced with a black dial). If it was bought 9 years ago it should be a 16570. You can see the difference in the font on the bezel. The 16550 has a more "computer" looking font, the 16550 should also have a 24 hour hand instead of a GMT hand, meaning, the latter is independent of the hour hand. Check the stacking of the hands, the 24 hour/GMT should be in the bottom. I would be careful if the magnification isn't looking good. As far as I know it should be the same for all Rolexes.
16550 - with white gold surroundings instead of black. Here also with a cream dial, only a few 16550 have that.
16570
