Has an AFL game ever ended 55-20?
Exactly once. On June 10, 1911, Essendon beat Fitzroy 55-20, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 55-20 in league history.
That makes 55-20 the 3836th most common final score out of 6,607 that have ever occurred in AFL. One point away, 56-20 has happened never and 55-21 has happened never.