Probably a typo, but an interesting one.
Remember the book and British TV series "Catweasel"? A 12th century wizard trapped in the 20th century after accidentally falling into a magical/holy well. His presence enabled a boy to have a variety of adventures, but his own quest was to work a magical spell to get him back to his own time. He had found a magical poem, which ended with the words "Look for where the Thirteen lies, and mount aloft the One Who Flies", and he took that to mean if he collected tokens of the twelve astrological symbols, then found a thirteenth one, it would fly him back to his own time. Each episode was an adventure that he and the boy went on, and he'd find a symbol at the very end. The boy's family were about to lose their manor-house due to poverty. At the end of the last episode, the Manor-house's clock was seen to have XIII instead of XII on its face, so the kid went up the stairs into the disused clock-tower and found a treasure-trove of gold coins that saved his family. Catweasel felt horribly betrayed because "the thirteen" was meant to be mystical, not a thirteen on a clockface lying/pretenting to be twelve to mark where the treasure was. He got home somehow, though.
But all my life I loved the idea of a number seeming to be a mere mistake, holding a deeper mystical meaning. So what do you make of XXII?
