Article by Emanuel Giordano 

There are many rumors that the Naihanchi kata was once practiced in Goju-ryu as well. Some of them even state that this kata was also practiced by Higaonna Kanryo sensei, known as the "renovator" of Naha-te. However, it is necessary to immediately clarify some points:
  1.        Although the topic lends itself to various speculations, the origins of this kata ARE NOT KNOWN.
  2. There is no evidence to support the modern theory, which points to Naihanchi as a kata imported from Higaonna Kanryo. 
  3. The oldest written sources include this kata in the specialties of the masters of Shuri and Tomari.
Among the various sources that indicate how this kata was practiced in Shuri and Tomari I would like to report two, the article Itosu no buyuden (Ryukyu Shimpo, 1915), where master Yabu wrote: "Master Asato belonged to the association for the promotion of these [martial] arts at Shuri and Tomari, which was part of Shuri at the time, and witnessing a performance by experts from the various neighborhoods, he himself ascertained that Itosu's Naihanchi was the best of all"; and the Interview with the venerable bushi Choki Motobu regarding true self-defense (Ryukyu Shimpo, 1936), where master Motobu compared the Naihanchi of two of his Shuri masters: Matsumura and Sakuma (both cited sources are available in full, and in Italian language, in the book Karate no buyuden - la storia eroica del Karate available at the following link: https://www.amazon.it/dp/B08TYJNYSP). Obviously there are many others, but there is no need to report them in this article.
However, the Naihanchi kata was also practiced in Goju-ryu, although in a much more recent era. In the interview with Anthony Mirakian sensei, published in Meibukan Magazine N°4, the master clearly stated that both Miyagi Chojun sensei and Meitoku Yagi sensei taught the Naihanchi kata, and that it was a kata commonly practiced in Goju-ryu over the years '50s, although it was never incorporated into the style. Anthony Mirakian sensei was a direct student of Meitoku Yagi sensei, as well as head of the Meibukan Goju-ryu school in the USA. There are also some rumors (which however need to be explored further) according to which Higa Seiko sensei, aided by his students Akamine Seiichi and Izumikawa Kanki, made several changes to Goju-ryu, including the addition of the Naihanchi kata.
Finally, it must be remembered that Miyagi Chojun sensei cited Naihanchi among the fundamental kata (along with Sanchin and Tensho), during the meeting of the Okinawan Karate masters in 1936. Why, therefore, did he not incorporate it (or not  maintain it) in his style? My theory is that he probably found it superfluous to add/maintain a third tanren kata within Goju-ryu, yet he still wanted to preserve the techniques. The most striking example is the Saifa kata, which contains several parts of Naihanchi shodan, albeit reinterpreted and slightly modified! However, Gekisai dai ichi (Fukyugata ni) is also partially derived from Naihanchi. It is my opinion that, in this case, it was a work of "reverse engineering", and that the kata was obtained starting from the basic bunkai of Naihanchi shodan (this similarity is evident to Shorin-ryu practitioners), then reworked in the kata we know today.
  • "Shorin-ryu Karate: kata 2" (here)
  • "Shorin-ryu Karate: kata" (here)
  • "Shorin-ryu Karate: The legacy of the bodyguards of the king of Okinawa" (here)
  • "The legend of the masters of Okinawan Karate: Biographies, curiosities and mysteries"  (here)