Mmm. Not sure about the wandering moon, the original source for that seems to be Drew Wagar’s fan fiction novels which are not canon for ED.
Nor is it clear to me what, if any, extent the ED RPG is canon for ED. It might be a clarification, or expansion, or just game-based invention. The ED puzzles should be self-contained within the game (I think FD produced the codex to answer the salt about that point) so I am dubious about such an external source.
The 50 year periodicity which John Harper referred to for Raxxla doesn't appear anywhere else as far as I can see, so I’d really like to know if it is at all canon. Doesn’t have to be a wandering moon, it could apply to a stealthy object orbiting a star, or a known orbit within a system if Raxxla is disguised as a known object. The stealthy object orbiting a star fits for Sol with asteroid 2060 Chiron, aka known as comet 95P/Chiron, since the asteroid/comet dividing line is a little fuzzy (pun intended, it’s as good as you’ll get at this time of day). And I believe FD have said comets are in game. Perhaps the real reason why they have not been visually depicted to date is that they don’t want to make Raxxla any easier to find?