Ultra-rare Wayne Gretzky rookie cards expected to be part of $3.72m Canadian auction

The case of trading cards was originally thought to be from 1980, until they were discovered to be from 1979, the year of Gretzky’s debut with the Edmonton Oilers. Photograph: AP

Among avid collectors of sports trading cards, rumours of a “holy grail” – a trove of cards so rare that they shouldn’t exist – have long swirled, but never materialized.

“It thought if we were ever going to find it … it would be buried deep up in Canada and the owners wouldn’t even know they had it,” said the expert Steve Hart.