"But there’s three worlds: There’s my world that I made up, there’s the licensing world that’s the books, the comics, all that kind of stuff, the games, which is their world, and then there’s the fans’ world, which is also very rich in imagination, but they don’t always mesh. All I’m in charge of is my world. I can’t be in charge of those other people’s world, because I can’t keep up with it." -George Lucas
So you have the creator himself saying it's a whole other thing, and that he didn't keep up with it.
Let me provide context to that quote with other quotes from Lucas:
“After Star Wars was released, it became apparent that my story—however many films it took to tell—was only one of thousands that could be told about the characters who inhabit its galaxy. But these were not stories I was destined to tell. Instead they would spring from the imagination of other writers, inspired by the glimpse of a galaxy that Star Wars provided. Today it is an amazing, if unexpected, legacy of Star Wars that so many gifted writers are contributing new stories to the Saga.” ~ George Lucas, foreward in rerelease of Splinter of the Mind’s Eye
“Over the years, many artists and designers have contributed to the articulation of the various universes of Lucasfilm. Taking their cues from the minimal words of description on a script page, these talented men and women have sketched, drawn and/or modeled creatures of magnificent breadth, unimaginable terror, and mind-boggling eccentricity. Some of these creatures have made it into film, while others, because of the way stories unravel, have not (so far). But this does not mean they do not exist. For once something is created, no matter what the context, it takes on a life of its own.”
―Foreword written by George Lucas in Monsters and Aliens from George Lucas
“George Lucas says “There really isn’t any story to tell. It’s been covered in the books, and video games, and comic books which are things I think are incredibly creative.” ” George Lucas Interview with the LA times May 2008
Seems to me that Lucas considers them canon, even if he can't keep up with everything- even going so far as to say that he doesn't need to tell more stories because of the EU. And major plot points had to be checked off by him. Some things were denied- details on the Jawas and Yoda's species? Didn't fly. Zahn originally wanted Joruus C'Boath to be a clone of Obi-Wan- Lucas shot down that idea. He had major involvement in many projects like Shadows of the Empire and The Force Unleashed, to say nothing of the Ewok movies he personally wrote (how does Disney justify ignoring those?).
And while there certainly have been retcons, retcons are not a sign of a lack of continuity- rather, they're a sign that there is an effort to amend continuity for the sake of strengthening it (that doesn't mean it always works, but there's definitely the effort).