Well, even Mees says in the introduction to his book that he is unable to disclose certain pieces of information given him in confidence. This is, of course, the manufacturing technology that is confidential regarding emulsions. The same is true of Fuji. Neither company will discuss many trade secrets.
I know that Kodak had an ISO 400 film in 1965, as I was one of the internal testers. But, an ISO 400 film was not released until the Fuji release in the early 80s or late 70s. The technology was on the shelf, but was not used until there was some urgency attached as in this case, Fuji released their film before Kodak did. This type of example might be what Mitchell referred to. But, I know of no advantage at Fuji over what Kodak knew regarding couplers, emulsions and coating. In fact, until the 60s, Fuji was using extrusion coating, and Agfa type couplers along with Konica and both companies were doing hard R&D to catch up with EK. We had reports that some of their organic chemists and emulsion makers were sleeping at the plant and working double or triple shifts to do the R&D work that would enable them to catch up quickly.
So, I think that this is an "outsiders" opinion based on a "feeling" not on fact. Maybe based on emotion as well. A frustrated person. IDK for sure.
You know that I know Tadeki Tani and have had lunch and dinner with him along with Paul Gilman many many times over the last 30+ years, and yet we avoid this type of trade secret stuff and just hint back and forth. I also know Yasuo Wakabayshi of Konishiroku and yet we avoided this type of discussion.
We were working on catalytic imaging in the 70s and Fuji and Konica were dying to know where the R&D stood and whether we were ready to commercialize the products under development (and which products), but we could not tell them anything. They pumped us very hard for information but we were not allowed to even direct them to a specific patent, and the same would be true of Mitchell.
OTOH, Byrd often came to EK to consult and was given a lot of information under an NDA.