I do not know if Akuzawa has actually recoved pure Yagyu Shingan-ryu essential training, or if he used the kata (shape) of their basic movements and "filled" them with discoveries of his own, an amalgam of all he's trained.
Great post, Ellis. My opinion, from personal observation (i.e., write it in pencil, not in pen) is that even within a small, but knowledgeable community, there is always some degree of adding and borrowing to the core knowledge, so if someone's "got it", the question of where they got it can become an interesting but not really resolveable discussion. Look at some of the better-known names in Aikido... some had it, some didn't, and many of them got their information from different sources and perspectives.... and the degree of "aiki", it's sophistication, etc., often varied considerably. One reason, IMO, why it's better to just encourage people to get what they can where they can and sort it out later.