I trained at Vasquez and Teshiba's dojo when they were based in Miami. He was rokudan and "Shihan." She was godan. They were both excellent instructors in my view, and I got a good vibe from the dojo. I think it's better than a Vegas or Altantic City slot odds to say that Pablo Vasquez is not Japanese. Before I went there long ago, I visited the website and was confused. I had though that each school had one Shihan, as the ASU does (unless Ikeda's label as "successor shihan" also means flat-out shihan). So, I was confused how Yamada Shihan shared that title of master instructor with advanced sensei in his own organization (USAF). Then there's the shidoin label, which I don't understand. Does someone?
Shihan has never been synonimous with leader of an organisation. In the USAF we have always had several shihans, even when this was restricted to the senior Japanese instructors. When I first started, the USAF-East had Yamada, Sugano and Kanai. I am personally more a part of Kanai's lineage than Yamada's for that matter.
For a brief explanation of shidoin and shihan, here are the relevant articles from the Aikikai International Regulations :
Article 15 : QUALIFICATIONS OF INSTRUCTORS
1. With respect to an Aikido organization with Hombu Recognition, the qualifications for instructors are as follows:
2. The titles for instructors' qualification are written in Japanese.
Article 16 : SHIHAN
1. The Hombu examines and appoints Shihan from among persons who are 6th dan or above, and who are proficient in practice and instructing.
2. To the appointed person, a Certificate of Appointment is awarded by the Hombu.
Article 17 : SHIDOIN AND FUKUSHIDOIN
1. An Aikido organization with Hombu Recognition is to have a system for qualifying Shidoin and Fukushidoin.
(1) Shidoin are persons of 4th dan or above
(2) Fukushidoin are persons of 2nd dan or 3rd dan
2. An Aikido organization with Hombu Recognition can issue a Certificate of Appointment to those whom it has appointed Shidoin and Fukushidoin.
3. An Aikido organization with Hombu Recognition must report to the Hombu the name and dan grades of those whom it has appointed Shidoin and Fukushidoin.