Oh, I don't know..
But I agree that it is nearly impossible to verify.
As I understood, he supposed, that you never could say, wether your Aiki was the same as someone else's, because of the nature of Aiki. He apparently told Kimura, that he weren't sure about this sameness in the case of him and his venerated teacher. But he didn't exclude that someone could reach the same level as his own, that's probably why he trained to the last day….
...very much like many others.
And here everyone may name his preferred figurehead.
In our quest for final historical accuracy, we may be doomed to fail, though at least a few of us have brought a shimmer of light into the world of contemporary budo, and this in an entertaining way....
Oh I agree that there is certainly room for historical research etc. I just don't think that research based on Sagawa is particularly useful, mainly because he was so private, but also he was so dismissive of pretty much everyone (including Ueshiba), and, according to his own long term students, he delibrately misled his students. He was pretty damning about Sokaku too BTW: I think he said that Sokaku had aiki, but nowhere near to the level that he (sagawa) had developed. So who knows what the truth really was?