Originally Posted by anabolism

SWUs have an expiration date based on when they are issued; it doesn't matter if the flight that caused you to earn them was in a previous year. I've seen posts from people deliberately leaving their FF number off tickets with the intent of claiming the flight after the new year, although the context was crossing a million miler threshold (if you do this as an EXP then you would not have EXP benefits for the flight).