An 1890 Act of Congress says these can be redesigned no more than once every twenty-five years.
Yeah, no. I don't know when that clue was written, but even excluding this century's designs I can come up with a solid counter example WELL before that clue would've been a glint in a writer's eye:
(It can be done even without relying on those 1976 commemorative reverses.)
Congress can still decide to redesign them whenever they darn well choose.
Quite frustrating to be able to legitimately rule out the 'correct' answer.