Due to the idiosyncrasies of O'Sensei (not pathologically paranoid like I believe Takeda Sensei was), due to changes in pre-war and post-war Japan, due to a host of other circumstances, it is practically impossible to assert that O'Sensei passed on all that he knew in any manner, shape or form, to any one of his students (including his son).
I'm reminded of an interview with Threadgill Sensei that I read a couple of months ago. (http://www.aikidojournal.com/article...light=Takamura
) He explained (paraphrasing) that even in a koryu, it is impossible for any teacher to pass down everything he knows. No matter how excellent the teacher or how diligent the student, one lifetime is never enough.
It is therefore one of the duties of each headmaster to add the results of his own studies back into the tradition. Every generation loses some things, but rediscovers others, and that's how the art survives.
The claim that all of Ueshiba Sensei's aikido was passed down (to anyone), and therefore our modern training as defined by his students (however capable) cannot be questioned is fundamentally bad for the long term health of our art.