Honduras, since 1866
Before 1866, Honduras didn’t actually have a legally defined national flag. It kept using the old Central American blue-white-blue tricolour mostly out of inertia. If you look on flag charts from that era they generally just don’t have an entry on Honduras at all.
Even after 1866 the five-star flag was only a merchant ensign, officially speaking. Flag charts from that time period, when they do show Honduras, almost always just show a plain blue-white-blue flag (or they get it mixed up with one of its neighbours). It wasn’t until World War I that foreign sources started consistently using the five-star version. In 1949 five-star flag was standardized and made the sole national flag.
September 1 is Honduran Flag Day.