Yagyu Shinkage ryu

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?

Yagyu MitsuToshi (the Yagyu family pronounces that kanji as Toshi with a T, not a Y -- so MitsuYoshi, although a more common pronunciation, is how "outsiders" say the name) was the man who studied with/received a license from Kamiizumi Isenokami Nobu(Hide)tsuna and is considered the "founder" of what's come to be commonly known as Yagyu Shinkage-ryu.

Yagyu Munenori was his second son and was recommended by his father to serve Tokugawa Ieyasu, the founder of the last martial government of Japan. He was both a teacher of swordsmanship and political advisor to Ieyasu and his son, Hidetada, the second Tokugawa shogun.

Yagyu Jubei Mitsutoshi (not Mitsuyoshi) served Iemitsu, the third Tokugawa shogun as kenjutsu shinanyaku (instructor of swordsmanship) as well as (according to legend), a "spy" -- so that's how all those stories of Yagyu-ryu ninjutsu came to be. Really, though, it's better to think of Jubei as an undercover inspector of conditions throughout the country.

Sugawara's book should be taken with a large dose of salt. A lot of the stories in the book are wrong in a number of details, if not in entirety. This can be expected when it comes to popular legends and so forth, so I wouldn't use it as a "source" of information. It's a fun read, but suspect.

[PiersonJ]

Just to clarify this for anyone who stumbles upon this via Koryu.com's link "A note on Yagyu Jubei"

Munetoshi received licensing from Kamiizumi Ise-no-kami Hidetsuna
Munenori was the fifth son of Munetoshi.

I apologize if you were quoting from the book, just clarifying.