As I see it, your headcanon is canon for yourself, but not for others.
It's difficult to explain, but basically, if you think something is canon, no one can tell you wether it is or not, because of multiverse bullshit. What may be canon for you may not be for others, and viceversa. Right now, I could tell you that your headcanon is wrong, and all you'd have to do would be shout "multiverse" and you'd shut me up.
