Forever. Literally. Just like your FIN number, it's is also forever - unless you change it to an NRIC after taking up PR or Citizenship. However, you can be that your old FIN number is also locked up in there somewhere as well.
SOME PEOPLE TRY TO TURN BACK THEIR ODOMETERS. NOT ME. I WANT PEOPLE TO KNOW WHY I LOOK THIS WAY. I'VE TRAVELED A LONG WAY, AND SOME OF THE ROADS WEREN'T PAVED. ~ Will Rogers