Take a look at the address bar in your browser and you will see a threadID=xxxxxxx
Your thread is number 171960. I would guess this is unique to a thread.
The earliest thread I can find is > click here < which is number 68966 I would guess all earlier threads have been... ahem... archived.. ;-)
I dought it started from 1 though so not quite accurate!
Maybe the FE will know for sure!