My question is about Yagyu Jubei. I have recently finished reading 'Lives of Master Swordsmen' by Makoto Sugawara. In it the author has a chapter dealing with each of the first three masters of that school. The name Yagyu Jubei is the one that I'm familiar with. The name is legend and has numerous fictitious characters modeled after this historical figure. (Ninja Scroll!) The author's chapter gives the historical name as Yagyu Mitsuyoshi, but refers to him as Yagyu Jubei twice. Once in the chapter about Yagyu Munenori his father, and once in the chapter on Ono Tadaaki.
My question is this; where did the name Yagyu Jubei come from? Does it have something to do with the Kanji characters used to make up the name? Is it some sort of Yagyu Shinkage-ryu secret?