BTW I doubt "most" aikikai groups give out their own dan certificates. My organisation, the USAF, certainly doesn't. It only awards Aikikai dans. .
Yudansha certificates of the ASU under Saotome Sensei come from the Aikikai Headquarters. The last round of certificates given by Saotome Sensei himself came when I got 4th dan. After that it's all been from the Aikikai.