As and example if you had CS with years subscription and not renewed the subscription; then 2 years later if I need to reinstall my OS cleanly; how would you able to install the original installation plus the years subscription which you paid for?
The subscription is valid for 1year from the date of activation. So, if you activated the software in year 1, used it for a year, did not renew it for the 2nd year and did a fresh OS install in year 2, then you would have to buy a new subscription from there onwards. HTH..