the devs research on TOE was thorough and they used a combination of documents to settle upon one. You can search the threads and this topic was discussed at length and depth. The devs gave a GREAT deal of specific info on this and many forum members contributed to the final result.
Got a link? Searching TOE and OOB turns up a lot of chaff...
you need to search the threads, and most was NOT online at the time. These were rigorous searches, academic level, not simply sitting in your office type. As in go to Naval Archives and LoC to read original documents. IIRC, one of the devs was in Japan at the time and got access to IJA records.
Again, some of this is now available on the internet (a fair amount released in the last 2 years, I'm still reading Nimitz' communiques), but at the time it was NOT available electronically.
Even though PaxMondo is correct in his response, it still underplays what the devs did.
JWE/Symon paid for out of his own pocket, for the professional translation from Japanese to English, of original Japanese source documents. So even if those original documents were to be located on the internet, your average AE forumite who loves to demonstrate just how superior their knowledge is compared to that of the devs, would still be none the wiser because they can't read the documents.
IIRC, it cost JWE something in the vicinity of $USD 100 per translated page. He used a professional Tokyo translation firm who regularly did his legal translation work as required.
Then there was the additional work done by the devs of directly corresponding with Japanese academics who held expertise in the area. Again a degree of professional thoroughness never undertaken by the AE internet know alls, legends in their own minds only whose only qualification is a working index finger.