Has an AFL game ever ended 31-22?
Exactly once. On August 15, 1908, St Kilda beat Fitzroy 31-22, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 31-22 in league history.
That makes 31-22 the 3836th most common final score out of 6,607 that have ever occurred in AFL. One point away, 32-22 has happened never and 31-23 has happened never.