When you're speaking about the history of Zelda, you want a standard set of unchanging documents to refer to. If there is no standard set of sources, there is no history. This is what canon material is: the accepted standard documents, out of which evidence can be pulled. Currently, I include the following things in the canon: Anything that comes inside the box, in all versions of the game. So, for example, with LoZ I include the game, the manual, and the included map. I don't include the text description on the back of the box. I don't include box texts because (1) I don't think the original game designers wrote this text, and (2) I don't think the American version of the box is translated from the Japanese version. I only include these things in the canon, because I think these are the only things we can trust to be relatively stable and unchanging. Other people, though, might include guides. I don't include guides for the same reasons I don't include box text.