If your tickets were first purchased on or after Feb. 12, 2017, they do now have an expiration date.
As of right now, tickets purchased within approx. the last year will expire if not first-used by Dec. 31, 2018.
Likely soon (MIGHT be as early as THIS coming Sunday) new tickets purchased likely will expire if not first-used by Dec. 31, 2019.
Once a ticket has expired, if never used, it’s original value can be used toward the purchase of NEW tickets at such time as you need those new tickets.