Really? Wow, you'd better not tell all the dojos affiliated with Shioda or Tomiki that.
The two biggest schools to come from pre-war students of Ueshiba. That's not to mention Mochizuki, either. I'm not sure how large Yoseikan is -- maybe they have more members in Europe, but I don't know.
When you get right down to it - Shioda, Mochizuki, Tomiki, and Kisshomaru Ueshiba all studied with Morihei Ueshiba primarily before the war and established their teaching styles after the war (Iwama "style" being one form that was clearly established post-war with post-war students).
So you could say that all of the major styles above (including the Aikikai under Kisshomaru Ueshiba - he took over from his father in 1942) are "pre-war" styles or that they are all "post-war" styles, or that the division itself is really somewhat artificial.