Verified answer

The ones you buy do not expire and can be used for new accounts or to extend existing accounts.

Trial ones do exir after a while and have their end-dates written on the card itself (if you don't see it then you're okay).

You can add upto one renewal card in advance to your subscription at a time. My subscription doesn't end until january and I have just entered a 12-month card (that is 3 years old - I got a good deal a while back)! The card is waiting on my account and will self renew the day my existing subscription is set to expire, on that very day Ican then enter another 12-month card's code and will in effect have 2 years subscription paid up and automatically covered.

Hope that helps with the explaination!

No they dont expire. Only if you use them, they would expire. Because it counts down to 12 months. You have to write a verification code to activate the account which can only be expired if the account is activated.