George S. Ledyard
For me, the easiest way to think about this is that there's a difference between pre-war and post-war Aikido as the art spreads and teachers mature and grow. It was during O-Sensei's time at Iwama with Saito Sensei that he really put the finishing touches on what would become post war Aikido Kihon Waza. It really was a "bridge" period. Saito Sensei would hold a copy of O-Sensei's pre-war book and say "see I didn't change anything" yet he didn't really look like Shirata, Tomiki, Shioda, or Mochizuki nor do they look very like each other.
As you say, Saito always maintained that he was doing things "by the book" - pretty much the same way that things were done in 1938.
He was close enough to Yoshinkan that Gozo Shioda asked him to follow him there, at one point.
The interesting thing about Shirata, Tomiki, Shioda, and Mochizuki is that they all started before
the war, when Kisshomaru started, but they all developed the styles that made them known after
the war, just as Kisshomaru did.
If you ask me, the difference in "post-war" Aikido is less the product of differences in pre-war training by Ueshiba himself then it is the influence of Kisshomaru and Tohei on the Aikikai.