Whenever I see reference to "lineage," I get a little amused. Up until a few years ago when I got "back" into karate, I never heard that term re: isshinryu. Introducing myself to a younger practitioner, he asked me my lineage. I was very confused. I searched my mind for an answer, and found only one - "Shimabuku lineage."
When I got my black belt, there was only one 10th dan "Soke." Tatsuo was still around. I believe my shodan certificate carried his mark. I don't believe there was anyone who claimed to be a 9th or even 8th degree at that time. To this day, while I follow my sensei in following Uechi, who followed Uezo, I still consider that we all share and follow the Shimabuku lineage and those he learned from.