There are several books about the Kojo-ryu, and I would like to examine what is written about it. From the old books, we have Karate-do Kyohan, written by Tominakoshi (Funakoshi) Gichin, published on May 25, 1935 (Karate-do Kyohan Reprint, May 26, 1985, published by. Kazusa Co.) The text is in Volume 1, Chapter 3. History of Karate, page 9, last two lines.
The contents are as follows.
Matsumura in Shuri was Matsumura Sokon (1809-1899). Maesato in Kume was Maezato Ranpo (1838-1904). It is difficult to identify which person was Kojo as there were many people in this age group. The person who was associated with Maezato was Kojo Shuren (1883-1945), but closer in age is Cai Changwei (Kojo Saisho) (1816-1906).
If they learned kata from Iwah, the three clans must have had the same kata, but Matsumura Passai, Useishi, etc., were not passed down in Kojo-ryu, and if it is a tradition of kumite, the same kind of kumite was not passed down in Kojo-ryu. Maesato and Kojo are both from the same Kumemura area, so there may have been an exchange between them, but Matsumura was from Shuri.
It is unclear from whom Tominakoshi (Funakoshi) received his information about Iwah or where they came from. It is also unclear if Iwah as a person ever existed in the first place.