wow. I can see your frustration. There are lots of conflicting and erroneous info floating around on these kata.
I did manage to find something that is semi-substantial that may lead you in the right direction:
here's the quote:
"The Kyokai does not recognize the Taikyoku (a Kata) and therefore it is not practiced by them. Kyokai says the kata was created by and perfected by Master Gigo (Funakoshi). But this is not true. The Taikyoku is the result of many years of training by many people. Mr. Kuguimiya (Takushoku) is one of those karateka. During the Second World War "Karate-Do Kyohan" was published (the Second Edition), book written by Master Funakoshi, as we all know. In the supplement of that book the author presents the Taikyoku under his own signature. Once that is said I call to your attention one thing: if the Kyokai considers Master Funakoshi as the highest technical counselor and it doesn't practice the Taikyoku, this would be incoherent."
-Master Genshin Hironishi.
President of Shotokai International Association with headquarters in Japan.
The last surviving 5th Dan of the 12 godan karatekas that existed by the end of the Second World War.
even the article on this site has conflicting info:http://www.fightingarts.com/reading/article.php?id=135
"According to Egami (14), of the original 19 kata of the Shotokan designated for study, the three Taikyoku Kata as well as the Ten no Kata (Omote and Ura) were all created by Gigo."
(14) According to Egami on Page 103 of "The Heart of Karatedo"
another conflicting source:
"Funakoshi Yoshitaka created the three Taikyoku Kata, the Taikyoku Shodan, Nidan and Sandan. The French Karate pioneer Henry Plee extended the system later by three Kata, the Taikyoku Yondan, Godan and Rokkudan."
...and so on the conflicts of info.
also to keep in mind:
Yamaguchi (Goju Kai) added to the Goju system modified Taikyoku Kata.
I tend to believe Hironishi's version of a study group. my best guess of the senior members of this group based on condensing references consisted of (but not limited to):
perhaps: Shimoda,Otsuka, Kasuya, Akiba, Shimizu and Hirose.
hope that helps.