Of course, the idea of all Gundam series being part of a single timeline makes absolutely no sense... The Wikipedia writers may know what Tomino was thinking or they may not - either way, I don't care, it's not the author's job to instruct his audience in how to interpret his work...
To me, the Dark History is simply an homage. It "unifies" all those stories by giving them a nod, a show of respect. I choose not to take it all too literally. It's more like he's breaking the fourth wall rather than literally putting all the timelines together into one...
Put another way - the characters in Turn-A have this Dark History - a long history of warfare culminating in the destruction of civilization - a history which threatens to repeat itself. But when we actually see it, it's made up of clips from old Gundam shows. As a result of that creative decision, first off, we recognize the Dark History when we see it. It's in our past, too, though we see it from a much different perspective. Additionally, it allows Turn-A to be something largely new while still serving as an homage to all Gundam on its 20th anniversary.
To me, that's a much more sensible and meaningful interpretation than taking it all literally and trying to figure out when Gundam Wing or Gundam X happened relative to Gundam...
