What I can tell you is that blurb for Figure 6-1 is originally authored by Drs. Smithuis and de Lange. However, there is a glaring error in it. It talks about segment 6 being divided into something (the rest of the blurb is covered by the hand), but I'm certain the blurb is discussing the Bismuth classification which does divide segment 4 into 4a and 4b.
Looks like it has nice pictures, but I wonder if those doctors ever got credit.