Peter A Goldsbury
Consider such a scenario. Both Takeda and Ueshiba allowed their deshi to attack them at any time, but it was also pretty well built into the equation that they would not be defeated. Takeda seems to have interpreted this convention much more strictly than Ueshiba--and I wonder, really, how strongly Morihei Ueshiba used to attack Sokaku Takeda. He obviously did, but the results were rarely recorded. Similarly, if you are a deshi and Master Ueshiba says, 'You can attack me any time', when do you, a relatively raw deshi, actually do this? When he is taking his bath, having dinner, or taking tea (the attack and defence being Araki-ryu style)?
When the deshi accompanied O Sensei on his trips to Shingu, or Kyushu, or Osaka, I do not think that making unprovoked attacks, in a railway carriage, for example, was in the forefront of their minds.
'Unprovoked attacks' at 'any time' were really a tatemae.
I thought there was just such an incident recorded in Gozo Shioda's interview in Aikido Masters. I don't have the book handy, so this is a somewhat hazy recollection.
I believe while travelling by train, Shioda sensei was wondering if he dared give Ueshiba sensei a whack while he appeared to be asleep. Ueshiba's eyes popped open and he said something like "A kami just warned me that Shioda was going to try to hit me".
So maybe not at the forefront of the deshi's minds, but the thought at least occurred to one of them.