Your theater wasn't enforcing the restrictions.Maybe there was a "Josh Steinberg Clause" in the RCC that wouldn't let you use the popcorn coupons day-of acquisition - they always worked for me!
Back when I went to Regal and cared about the rewards, I remember getting those type coupons: free something good for next viewing type thing. It depended on the local theater as to whether they were enforced. Similar to how some stores care about coupon expiration dates and some don't.