Has an AFL game ever ended 75-20?
Exactly once. On July 30, 1898, Essendon beat Melbourne 75-20, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 75-20 in league history.
That makes 75-20 the 3836th most common final score out of 6,607 that have ever occurred in AFL. One point away, 76-20 has happened never and 75-21 has happened never.