There is a difference between the WAT chart limits and the HV. Hopefully you are well clear of the WAT chart anyway - the HV is the one that's difficult.
And you are right, there isn't a lot of help in interpreting the charts.
The 9 passengers or less limitation is on the configuration, not the number of seats you have occupied. You can see this in the change in the HV location on the BK-117 when it goes to a high density seating configuration - the HV curve moves to the limitations section of the supplement. S-76 with the less than 9 pax supplement has the HV curve in the performance section.
The problem is that most of the helicopter community doesn't understand that Part 29 helicopters are supposed to offer the same level of safety as a Part 25 airplane- that's why they are in that category instead of Part 27.
Which brings me back to my original question - why not use the CAT A techniques and performance stuff- the profiles are pretty straightforward, not much of a performance hit, and guaranteed to be able to fly away or land back if the engine fails?