Well the first
doshu was Morihei Ueshiba, so he was probably around most of the time that he was teaching
The second doshu (Kisshomaru) wasn't doshu until 1969, at which time Morihei wasn't around all that much...
Kisshomaru took over the Kobukan in 1942 after training with nobody but his father and some Kashima Shinto-ryu instructors. There were people around after the war who were senior to him (that doesn't include Koichi Tohei), but he didn't spend much time training with them - he did spend time training with his father in Iwama (where one of his early students was Morihiro Saito) and Tokyo. Whose tradition did he represent, if not his father's? Certainly, he spent much more time training under his father than his father spent training under Sokaku Takeda, but nobody disputes the fact that Morihei was Sokaku's student.
Did some things change? Sure. Even in the most archival of the archival arts I can show you places where things changed. The real question is whether or not you believe that such changes are in line with the scope of the transmission.