It's important to cover all possibilities.

Marty McFly: That's right, Doc. November 12, 1955.
Doc: Unbelievable, that old Biff could have chosen that particular date. It could mean that, that point in time inherently contains some sort of cosmic significance. Almost as if it were the junction point for the entire space-time continuum. On the other hand, it could just be an amazing coincidence.

Back to the Future, Part II