Canon can be split into three categories, "Canon", "Non-Canon", and 'Anime Campaign".
Canon
Canon is the Epithet Erased Show and Novels, as well as any supplementary media that does not contradict it. If there is a contradiction in canon (ex: Meryl also being on dispatch in EP 5-7 Novelization contradicts the conversation in "Redwood Run" between Percy and Eros), we would find a solution to amend it whether it's ignoring one, acknowledging both whenever it appears, or finding a less than obvious to make both true.
Unknown Canon
In cases where a piece of media's canonicity is unclear, it is assumed to be canon. That is a piece of media that does not contradict the Canon media but is not confirmed by Brendan Blaber (or another crew member) or by Canon media itself.
Non-Canon
Non-Canon is any media said to be non-canon, like TWO-LOWEEN, or can't be Canon due to contradicts, like the ads involving the Epithet Erased dolls. Although information revealed in them may be taken as canon (at least in the case of TWO-LOWEEN where it was said to be the case) but not the main events of the story.