For details on the opinion of the "certificate of the art of war using a long-handled sword in the Hokushin Itto-ryu style" being a certificate for long-handled sword, refer to "My First Sight of Ryoma SAKAMOTO's Letter and Certificate of the Art of War Using a Long-handled Sword in the Hokushin Itto-ryu Style" by Tsukasa MATSUOKA ("Japanese History" 454, 1986) and "The Hokushin Itto-ryu Style and its Full Mastership" by Haruo DOI ("Encyclopedia of Ryoma SAKAMOTO" Shin-Jinbutsuoraisha, 1988).
ちなみに、「北辰一刀流長刀兵法・目録」が薙刀の目録であることについては、松岡司「初見の坂本龍馬書状と北辰一刀流長刀兵法目録」（『日本歴史』454号、1986年）、土居晴夫「北辰一刀流とその免許皆伝」（『坂本龍馬事典』新人物往来社、1988年）が詳しい。