The DOT (not FAA) ruling requiring 5 year expiration period for compensation credits became effective last October. Specifically, it applies to situations where there is a significant delay or cancellation and the airlines offer a credit as an additional option to the now required automatic refund option (which now is supposed to happen if you don't otherwise communicate with the airline about your flight and don't take it). So it sounds like OP had some sort of significant change (3 hours for domestic itins and 6 hours for international) to ticket which also made it eligible for a refund.

https://www.transportation.gov/brief...ic-refund-rule