Nice catch, Ed.

Of course, the 1939 version of Batman was from Earth-2, an Earth where all fictional events happened 20 or 30 years earlier than on Earth-1. So maybe their movie industry was similarly time-shifted? In that case, the Fairbanks Zorro came out around the turn of the century, and the Power Zorro did come out in time for Dr. and Mrs. Wayne to attend it.

Now, what Earth the events of The Dark Knight Returns happened on, that's anybody's guess. If it was Earth-Miller, where Detroit was still making cars with tailfins well into the 1990s, then all bets are off as to when the various versions of Zorro appeared!