I thought I'd repost this up top here, because it seems important:
I would propose these as our official "Canon Categories"
Category 1: Canon
Type A: Release info
Official Bungie-released materials. (Games, manuals, comic)
Type B: Trans-release info
Information that is both pre- and post-release pseudocannon.
Category 2: Pseudocannon
Type A: Post-release info
Bungie-sponsored released materials. (GURPS, Chimera)
Type B: Pre-release info
Unreleased Bungie materials.
Category 3: Noncannon
Type A: Legal "canon"
Materials not directly sponsored or produced by Bungie, but authorized by later, non-Bungie legal stewards of the Myth franchise. (Myth 3)
Type B: De facto "canon"
Materials not directly sponsored or produced by Bungie, but generally accepted by the Myth story community and well-supported by evidence from Categories 1 and 2.