Mis-date, which means to incorrectly assign a date to something, has several antonyms. The first is "accurate," which means precise, correct, or exact. If something is accurately dated, it means that the date assigned to it is correct and free from errors. The second antonym is "valid," which means legally or logically sound or justified. If something is validly dated, it means that its date is lawful, fair, and correct. The third antonym is "authentic," which means genuine, original, or truthful. If something is authentically dated, it means that the assigned date is true, honest, and reflects the actual time of the event.