I believe it is a 'human construct' that only discusses a certain level of experience. The thing that isn't highlighted as much in discussions as history are the realizations of nature that O'Sensei experienced and was profoundly transformed through. These are not historical experiences, but personal and phenomenal experiences. They are moments of re-defining all that went before and putting them in to practice. As in the quote,when was aikido developed.....'when I was born'. You could still do all the same moves, but with a new realization they can become fastened to another level of knowing. And through practice this exchange of form and insight become a continuous cycle. That is how I know I'm doing aikido and not just waza. That is the remarkable element of aikido, for me. Same moves, different understanding.
This is exactly why in Yoseikan we can learn Karate and Judo techniques, but we are still doing Aikido.