Albert, I guess there is a sense in which this is my definition. I was attempting to put into other words how I have seen the term "steal" used in jazz contexts. You may be right in thinking it in appropriate usage, or a usage, at least, that is too different from more established ones to have merit.
No, I don't think Nichols stole from Bix. Bix didn't succeed because of his own problems.
Sorry you are offended by my terminology. I did use the word "steal." Perhaps I should have said instead that black musicians were not given appropriate recognition, status, or monetary remuneration for their artistic creations, and left it that.
I didn't answer all of your questions, but I hope this helps.