Has an AFL game ever ended 78-17?
Exactly once. On June 1, 1901, Geelong beat St Kilda 78-17, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 78-17 in league history.
That makes 78-17 the 3836th most common final score out of 6,607 that have ever occurred in AFL. One point away, 79-17 has happened never and 78-18 has happened never.