Bob, I don't keep current on the speed stuff, but I can quote from ANSI PH2.5-1972 {"…Method for Determining Speed of Photographic Negative Materials (Monochrome, Continuous-Tone)"; dated 1972} if that helps any. Some of the key points are reaffirmed in the 1997 IS&T Handbook of Photographic Science and Engineering, which is probably about as close to a bible as the photographic industry has. They say the same speed formula "… is also adopted in International Standard ISO 6…". I doubt that anything significant has changed since then. In fairly recent history, the changes (ANSI) seem to have been things like moderate changes in the pH and buffering capacity of the developer, etc.(posted 8171 days ago)John Hicks says, "That's been changed [specific developer, etc?] and manufacturers can use whatever they want... …". He may know something about this that I don't, but I think it's more likely he's heard something about COLOR negative standards and mistakenly presumed they were a change to the "monochrome, continuous-tone" negative standard. (Please correct me if I'm wrong, John.)
Basically, Frances Shultz' quote (in your excerpt) seems to be pretty much correct. That is, the film is developed such that when 1) you find a point on the "characteristic curve" that has a density of 0.10 above "base plus fog" and 2) you move 1.30 units over on the log(10) exposure axis the film density has increased by 0.80. On such a sample, the 0.10 density above base + fog IS the speed measuring point. This represents, to me, pretty "normal" contrast; a slope of about 0.80/1.30 = 0.615 if it were a straight line. Note that the 1972 ANSI standard specifies the delta 0.80 +/- 0.05.
FWIW, Richard Henry, in his book "Controls in Black and White Photography" has a fair amount of history on ANSI/ISO speed (monochrome neg film) standards. He indicates that some of the developer changes (pH, buffering, etc) had to do with the specified formula producing erroneous speeds on certain films. I don't have any good ideas on what you are seeing but this could be related. There may be errors in manufacturer's ANSI/ISO ratings on film, but I doubt it.
FWIW, the 1972 ANSI standard (and I presume all the more recent ones as well) addresses many of the variables in the system. As an example, the test sample must have reached equilibrium at 20 deg C and relative humidity of 60% +/- 10%. The light source is specified, exposure time must be between 1/20 and 1/80 second, holding period between exposure and development is specified, etc, etc. The developers of the standards are more savvy than many people give them credit for.