At least with the U S affiliates of the JKA, I believe that a minimum of a 6th dan must be on a panel to evaluate and recommend promotion to any black belt rank. The board (or a single examiner) directs the test, scores the applicants, and sends the package to world JKA HQ in Japan. The dan certification (and your wall-hanger) actually originates from the JKA organization in Japan. Until recently I believe that there were no (JKA) non-Japanese 6th dans in the U S, so every JKA black belt exam was conducted by a Japanese native. There now may be two U S (non-Japanese ethnicity) 6th dans, who can - I think - examine and promote to at least 1st dan, and possibly higher.
The ISKF, based in the U S but headed by a trio of Japanese old-time Shotokan masters, has broken away from the JKA. I presume a ISKF exam is still headed by one of the principle seniors, but obviously, the certificate comes from Philadelphia, since ISKF is no longer affiliated with the parent group in Japan.
There is a similar situation in say, Great Britain, where there was a split after Enoeda Sensei's death.The KUGB broke away from the JKA, and now are in effect an independent organization. So, a KUGB student - again, I think. These things change - receives a black belt ranking not from the JKA in Japan, but from the KUGB. At the time of the split, some of the KUGB kept an affiliation with the JKA, and that group is now called JKA-England, headed by Ohta (Ota) Sensei.
It may be there are more schools in breakaway groups in Shotokan karate than there are schools remaining in the JKA. Some are based in Japan still, others in the U S or Europe.