剣さばきの秘訣は、数人の優遇されていた弟子(石川主税、青木城右衛門、竹村与右衛門、松井宗里、古橋惣左衛門)に限定された特権ではなかった。彼らは全員が優秀な剣士であった。 五輪の書 と 兵法三十五箇条 は、寺尾兄弟への贈答として贈与されたが、実際に各弟子に伝えられたのは、生と死という不可解な問題を、断固として明らかにしたいと言う自身の決意だった。 そのような精神的な遺産を背景に、巨匠の教えによって、独自の規則、証明書、卒業証書を備えた実際の学校が生まれることはできなかった。武蔵は自分の技術を教えたり助言を与えることができたが、最終的に自分の力を測り、自分の道を評価し、そのために自分自身を適応させてゆくのは生徒自身の責任だった。よって、武蔵流は今日でも教えられているが、実際の内容は、二天一流の創設者と同時に姿を消したのであった。それ以外にどのような可能性があっただろう?柳生利厳は、尾張で教えたとき、こう宣言した: 「武蔵の剣さばきは、武蔵のみが可能な技で、他の誰も、武蔵同様に優れた剣使いをすることは不可能なのだ。」

Wikipediaの該当部分の日本語の文章を抜き出して英訳し、それを元にGoogle Books等で検索したのだ。

There were, however, no special secrets of swordsmanship passed on to special students. His disciple Furuhashi Sozaemon makes this clear in the
following statement:

Musashi passed away on May 19, but he called the three of us [Furuhashi and the Terao brothers] together on the twelfth. He told us that he supposed we had written down various things he had discussed every day concerning the martial arts and that we would be using them as memos. Nevertheless, there was to be no secret book for us and so he asked us to burn those notes and to throw away the ashes.

Thus, while The Book of Five Rings and The Thirty-five Articles of the Martial Arts were given as gifts and mementos to the Terao brothers, what Musashi really passed on to each student was his own spiritual resolution to solve the matter of life and death.
With such a legacy, a true school with rules, degrees, and diplomas could not be founded. Musashi could teach his techniques and give advice, but in the end each disciple was required to assess his own strength, find his own Way, and make that Way truly his own. So while the “Musashi style” is still taught today, the actual lineage of the Niten Ichi-ryu died with its founder. It could have been no other way. As Yagyu Hyogonosuke observed when he was teaching in Owari: “Musashi’s sword is for himself alone; it is not something that could be taught to other people.”