I agree and would like to add, there really isn't a Gwent canon. Gwent is a game that exists in the Witcher universe, (much like chess in our universe,) that uses names and spells from the in game universe. People like Geralt, Yen, Dandelion, etc... are quasi famous in the Witcher world, and the cards reflect that fame. Dettlaff's involvement in the events of B&W would be the thing of local legend. In the real world we know CDPR makes the canon, in the game it is a Baron in Toussaint who added SK to the game. Likewise it would be in game people who create new cards and rules and submit them to the other nobles.