I have the volume that says, "1600-1868" so it may not be exactly the same edition like the one featured here since I understand that they also have "1868-2000" coming out later as a separated book also.
Although this may seem like the authoritative book on sources of Japanese tradition for most English-speakers, and I must say it contains a lot, I still have my reservation. May be I'm a specialist that's why I think it overlooks some important Bushido literature, Budo Shoshinshu, that in fact was the more popular one it its time, the Tokugawa Period, than its sister publication, Hagakure, which became notorious only during World War II.
While Budo Shoshinshu was not even got mentioned at all, they devoted a whole chapter on Hagakure. In light of this alone, I sincerely believe the compilers simply miss the whole point if they really want to call their book, source of Japanest tradition.