I appreciate this video in the original post.
The book, The Making, has gone from an anticipated interesting read, to a must-have.
The historical analysis seems reasonable, compassionate and fair. Its focus on the documents, the rules themselves, and how these rules actually functioned in practice, feels accurate and useful. Both Gygax and Anderson are vital.
It convincingly demonstrates that "Dungeons & Dragons", per se, originates in year 1974. But the book explains the formative years leading up to it are innovative and causing a revolutionary paradigm.
It is interesting how the "rights" to certain historical documents can interfere with the process of understanding history. The authors are aware of this, and make an effort to compensate for the missing documentation in their description.
The book looks to be an excellent book about D&D, and even an excellent example of historiography itself.