Ueshiba's life was pretty well documented and his whereabuts and coming and goings have been checked and cross checked.
This is a repeat
Aikiweb Interview with Stan Pranin
AW: O-sensei also reportedly studied a lot of other koryu arts outside of Daito-ryu.
SP: I would say that that's not true.
If you look at it historically, he went up to Tokyo in 1901 and spent about a year there. During this stay in Tokyo when he was training to become a merchant, he did a little bit of Tenjin Shinryo-ryu jujutsu. It was probably a "machi" dojo, in other words a small dojo in the Asakusa area of Tokyo. He would go there at night, but it was probably about three or four months total since he got very ill with beriberi and had to leave Tokyo and return to Tanabe. He was doing it while working very hard during the day and it was a very brief period of only a few months. It would be difficult to imagine that that had a strong, technical influence.
By the same token when he was in the army, he also began studying Yagyu-ryu jujutsu. There are some questions about what the actual name of the art was. O-sensei referred to it as Yagyu-ryu jujutsu, while [Kisshomaru Ueshiba] Doshu did some research and said it was Goto-ha Yagyu Shingan-ryu or similar name.
He was in the army at the time and also was sent to Manchuria for a part of the time. It was hard for me to imagine him going regularly while being in the army, so I don't know if his training was on the weekends or what. He apparently was enthusiastic about his training but there just weren't the circumstances to allow a detailed study.
He did, however, continue to study a little bit of Yagyu-ryu after he got out of the army, but he was in Tanabe which was a couple of hundred miles away and he had to go up by ferry! Again, maybe he went up three, four, or a half a dozen times, but it wasn't the sort of thing of an intensive study with someone year after year.
Now, he did have a makimono (scroll) as well -- however, it bears no seal. One can only speculate what that meant. Sometimes what happens is that a person would be told to prepare a makimono or have someone prepare it and, for whatever circumstance or reason, the teacher never gets around to signing it. Therefore, the scroll cannot be considered official.
So, it would appear that he did study this Yagyu-ryu form more than the Tenjin Shinryo-ryu jujutsu, but probably at the most he did a year or two.
The other art that he studied, but again not in very much depth, would have been judo. The first description of the teacher who was sent down from the Kodokan to Tanabe by O-sensei's father to teach Morihei and various relatives and friends gave the impression that this judo teacher was somewhat of an expert. It turns out he was 17 years old. I met his wife back in the 1980s and she told me this directly. He could have been a shodan, maximum. Also, O-sensei was involved with other things in this transition phase of his life trying to figure out what he was going to be doing as a career. One of the reasons, according to Doshu, that this judo person was brought in was to help him focus and channel his energies. But O-sensei ended up going to Hokkaido.
So, you have
a. this very brief stint in Tenjin Shinryo Ryu,
b. some training in Yagyu Ryu jujutsu while in the army,
c. a smattering of judo,
d. (20+years) In Daito-ryu.
That's it. The impression that he studied many different arts other than Daito-ryu and mastered them is completely false.
Stan was pretty clear
I always look at these debates and ask a simple question.
Q: Had he studied all these arts, why was it, on that auspicious day:
1. when he was ready to hang a shingle
2. when it came time to make his mark
3. Why did he open the door and choose to teach and hand out scrolls in......
And that for approx. 16 years. You know all those Pre-war deshi supposedly doing Aikido up to 1938? They were all ranked in Daito ryu by the old man himself. Why? Because it was all he really knew.
And when he completed further research later on and arrived at the end of all things in his life the old man never waivered, and never changed from his first roots in aiki. He still only referred to his power as Aiki.
Ueshiba was an aiki man through and through. He said it himself. "Takeda opened my eyes to true budo."And he, like all of Takeda's men before and after him- was still an Aiki-man through and through at the end of their careers.
As a group; all five of them were living legends.