The term ‘Soke’ is not used in Shinto Muso-ryu Jo. And there is no single Headmaster either.
Within Shinto Muso-ryu Jo there are actually numerous valid lineages today, and not a single headmaster, as is found in some other Japanese koryu martial systems. ‘Menkyo kaiden’ is the style’s highest level of recognition and these exponents are the only people qualified to teach and promote other exponents of Shinto Muso-ryu Jo.
While it is not unusual today to have more than one menkyo kaiden within a group, organization, or even a dojo, the reality is that each one of them is able to make their own decisions about how/where/why Shinto Muso-ryu Jo should be transmitted. If we look at the history of Shinto Muso-ryu we can see that even near the beginning there were several menkyo kaiden involved.
After the Meiji Restoration and the spread of Shinto Muso-ryu outside of Kyushu, eventually several people (many Japanese and a few foreigners) have received menkyo kaiden. And those people continue the transmission of Shinto Muso-ryu Jo as a valid lineage.
Phil Relnick Sensei was the first foreigner to receive a menkyo kaiden, and the lineage information found on this website (/Jojutsu/Our Lineage) simply reflects OUR line of study and transmission of Shinto Muso-ryu Jo.