Just a note, while there was not a "cadre" of masters Motobu taught, there are a couple of notables: Isshinryu founder Tatsuo Shimabuku (for a short time) and Matsubayashi Shorinryu founder, Sochin Nagamine The latter provided an earlier quote of mine attesting to the fact that Motobu had appreciation and respect for traditional kata. (Yes, I've read his book you referred to.) Little karate history can be attributed to primary sources due to its secretive nature and the cataclysm of WWII. There are just a handful of such and thus highly valued. What largely remains are legends and orally transmitted stories no doubt embellished over the decades, though often with some spark of, if not truth, at least of value as illustrative myth.