Bill, I can tell the difference between a lens whose aperture doesn't open fully and one whose aperture is stuck. That wasn't the problem.
Angenieux and Nikon have long and good histories. When either specifies a lens' geometrical aperture, I believe what they say.
The R10 might bleed a lot of light off into the viewing optics, since it has an integral beam-splitter, but other S8 cameras with beam-splitters in the light path don't have this problem. Beaulieu S8 cameras (except the 1008 and 1028, which are rebadged Japanese cameras) have mirror shutters, lose no light to the viewing system; with the shutter open the film gets all of the light, with the shutter closed the viewer gets all of the light. As a result, when the camera is running the image in the viewer flickers.
Re what the standard says (and I haven't gone looking for it), given a 4008 ZM with an Angenieux 8x8B, what would you do to get good exposure when the onboard TTL metering system dies? I don't see a better way than testing with narrow latitude film. If there is one, I need to know about it.