Well, I had a reward that is set expire today (6/1). When I look at my Starbucks rewards dashboard, it is now gone. So, *maybe* they changed the policy and you now have to use your reward BEFORE the expiration date?
Also of note...I can't go back to April to see my Rewards History for that month, since you can only view the current month (June) and the past month (May) there. I earned the reward in April.