Mangaka do that all the time. Just because they designed the character doesn't mean they officially belong in the main universe.
I'm repeating myself, but my rule is, if the original author conceived that character, they are canon until stated otherwise within the overall universe, because I'm not nearly arrogant enough to be like
"No fuck you mr Author who created the series, I, a random fan decide what is canon."
That doesn't mean non-canon characters can't become canon (In the case of Bardock), just that I'm not going to dismiss the canon status of a thing the author came up with just because he didn't include it in one version of the story.
Otherwise there's no point to anything being canon if we're dismissing things over a technicality.