All the books that came with ED are canon. Some minor details regarding the Thargoids were changed later, so a few bits in ‘Out of the darkness’ and ‘And here the wheel’ are probably a bit of.I (don't) like how the books that came with the games, that introduced the dark wheel and raxxla, are not considered canon at all.
The timeline and stories from FE:2 seem to be the backbone of ED history. Some of the FFE stuff has caried ower as well.
The massive use of clones and androids from those games have been toned down significantly.
The Dark Wheel and probably also Imprint are not canon in the way that they accurately describe events that really happened, but they are considered to be stories that are known in the ED galaxy. MB explained that TDW should be considered an ingame legend.
This would put it in the same boat as Astrophel and Stella and make it valide as a clue source.