I agree with you that star systems inaccessible through normal game-play are likely not relevant to the ARG, nor required to explore. I therefor think discussion of shadow systems or phantom systems likely belongs in a different topic.
Understanding a bit of the mechanic behind it is useful in determination of any hex code provided to possibly be valid though. I have done extensive research into the shadow realms for a long time as some of you are likely aware. If anyone is interested, feel free to check out some of my main findings in an old archived topic: Shadow System Research - #30 by DevilinPixy
I would like to keep an eye on those hex codes though, considering they certainly have the potential to be a valid system by default (in any of the galaxies for that matter, as that value is not specified with this hex format).