Well from what I know every book (yes even the novels at the beginning) started off with permission from Capcom were official and they followed that game's plot.
However the DMC1 Novel surely is off now since it showed some things about before Dante opened "Devil May Cry" and how he got Ebony & Ivory. Even Vergil was in it. So with DMC3 coming in its place that story didn't stand as cannon anymore.
For the DMC2 Novel I haven't a clue. It's supposedly a bit before the beginning of DMC2. But for a reason when DMC3 came on sale it automatically along with the 1st Novel declared non-cannon by Capcom.
I think the artist just learned the events of the game and did the job on his own, but there's no clue if Capcom asked him in order to fill some DMC3 plot holes (like how Dante knew instantly that Vergil survived from the assault of devils that killed their mother) or just happened to actually do that (the filling) as a matter of sheer luck.
Perhaps it's both.
I suppose that's why the 3rd attempt was a Manga rather than a Novel. And as the others it is done according with the DMC plot and was published after Capcom agreed with it
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)