When the term "canon" is used in context of a work of fiction, it typically means any work related to the original and created by or accepted by the original creator as an authentic part of the over all story of the fictional universe he created. All this crap about a-canon b-canon c-canon is BS used to legitimize the fact that ol' boy George wants to pull in more dough by accepting royalties from the selling of liscened SW novels, but also doesn't want to be confined by rules or events related to those novels. Which is fine, but why not disregard them as canon altogether, instead of this "different levels of canon" stuff. Canon is suppose to be what is offically accepted, it either is or is not.
That said, when we talk about real canon, it is what Lucas and official sources make it out to be. Sure, I mentioned my personal canon, but that is just a fancy way of saying the works I wish to accept as having happened in my own personal experience of the franchise. When we start changing the meanings of words, such as "canon" to mean what is most plausable or what makes the most sense, or what was set out first, we muddle the meaning to the point where it is no longer a useful word.
The common understanding of canon in fiction (the understanding you're citing) is based on the mistaken view that the "creator" or owner always puts out genuine stuff or knows best what's the real thing. The idea at the core of the idea of canon is what's the real thing. That's what's at the heart of it. People have just gotten used to accepting that the word of the "creator" is the best guide to what's the real thing. But it isn't.
In its core essence the idea of canon (and thus the meaning of the word canon) is about what's the real thing. But you won't get the real thing if you go by a bad guide like the judgement of a "creator" who's lost touch with the work. Defining canon is all about defining what's the real thing. All this stuff about the offical line and canon being stuff created or accepted by the creator is about looking for the real thing. People are effectively just figuring that the offical line and stuff created by or accepted by the creator IS the real thing. But it isn't always.
And insisting on something being the real thing before recognizing it as canon is not changing the meaning of the word, it's holding to its core idea at the expense of its common interpretation. The whole idea of canon was created to define what was the real thing. That's what canon is all about. All this stuff about canon being what the "creator" says is canon is really just a descendant of that.
I'm not changing the meaning of the word, I'm just isolating its core meaning and insisting that anything called canon live up to that.
Things totally at odds with the core canon or drastically inconsistent with it cannot be canon. No matter what the "creator" says. Let's say Lucas gets up tomorrow and says the Care Bears tv show is canon in the Star Wars universe -it would not make it so. By the same token, the SE with its cartoonish stuff and the PT with its cartoonish stuff and fake Anakin cannot be canon. They are not genuine Star Wars.
The word canon is not rendered useless by recognizing its core meaning and using that core meaning as a criterea for judging what's canon. We may have to recognize that people may have different definitions of canon and different uses of the word, but that is true of many words in our dictionary and that does not render them useless. (And that is the situation with the word canon already anyway -you will not get everyone to agree on what canon is, there are multiple interpretations.) The word is made more useful when we are more faithful to its core meaning, because then we're talking about something real and not some silly idea some "creator" has.
I refuse to accept George Lucas's definition of Star Wars canon, because I believe that definition is at odds with the whole purpose of the idea of canon.
Many people share my view that canon isn't always what the creator says is canon.