If there is no availability now keep calling and checking - you don't have to pick the benefit until January 2017 (I believe).

So you can hold off on choosing which benefit you want until closer to the time. Keep an eye on seats, keep calling and checking. If it opens up pick the benefit and have them apply it.

If it looks like a lot of seats are open closer to your flight then wait list and roll the dice, maybe you'll get lucky.

Remember they expire a year from when you choose them so I'd wait until the last minute you need them or when you have confirmation of availability.