I can confirm that it's only at the gate and at the Guest Svcs location in Downtown Disney. I just did it recently.

I can't remember when they went to expire-no expire tickets. But, if you look on the back, it will say how many days were on it to start, and if it's after the switchover to expire tickets, it will say "no expiration" on it. At the time they started, the option was much less expensive than it is today.

If it was before all this, the tickets never expire and they are all considered park hoppers.