Has an AFL game ever ended 51-19?
Exactly once. On August 20, 1898, Geelong beat Melbourne 51-19, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 51-19 in league history.
That makes 51-19 the 3836th most common final score out of 6,607 that have ever occurred in AFL. One point away, 52-19 has happened never and 51-20 has happened 1 times.