There are a few errors I know of in my book, Hidden in Plain Sight
, most notably regarding the Shinkage-ryu menkyo that Takeda Sokaku gave Ueshiba and an error regarding a citation from the Kojiki - but that aside, the information in the book is pretty accurate. There is a very long chapter, A Unified Field Theory: Aiki and Weapons, that breaks down all that is known, to date, regarding what weapons and weapon-systems Takeda Sokaku and Ueshiba Morihei trained. There is surely more, particularly regarding Takeda (where did he learn kusarigama, for example? His son says that he would teach people things apart from the "aiki arts" that he learned in his travels), but everything in HIPS is either straight-forward, or in examples such as the question of Kukishin-ryu and aiki-jo, clearly shows the avenue for further research.
A lot of the same ground is gone over and over again in discussion like this one, using such poorly researched books as Aikido and the Dynamic Sphere
(it was a pioneering work, no doubt, but relied exclusively on such English language sources as Black Belt magazine). Ueshiba did NOT study "Yagyu kenjutsu" from Nakai Masakatsu. He studied Goto-ha Yagyu Shingan-ryu taijutsu
for several intermittent years. It is almost sure that this was primarily the jujutsu component, as there are no elements of Shingan-ryu kenjutsu or bojutsu in Ueshiba's methods.
In fact, in an interview which the interested can find on Aikido Journal, Ueshiba explicitly says he studied Yagyu-ryu jujutsu.
(People might save some time by having a look at HIPS, and starting the discussion from there. Just sayin')