I don't know the answer to your question but I will say that my daughter just received a diagnosis of HFA and was given the ADOS....the scores weren't even discussed in the report, it was more a description of what she had difficulty with and what things she was able to do easily

My son got a high score on ADOS (and CARS, too) but he needs few if any supports these days. I would characterize the ADOS as measuring autism-specific behaviors; that is, it includes those observations that best distinguish autism from another issue such as intellectual disability or ADHD or anxiety. The ADOS is designed to maximize the chance of getting the right classification (autism yes-or-no), I think originally they tried to make it agree with expert judgments. So it's sort of a translation of what historical autism experts would look for to make the diagnosis, into a standardized process.

The way ADOS is set up, the score isn't that meaningful as a dimensional trait. The point of ADOS is the cutoffs rather than the score.

The items they choose for ADOS are ones they're hoping will distinguish a person who is intellectually disabled, anxious, shy, etc - but not autistic - from a person who is autistic.

The items on ADOS don't necessarily relate to "functioning"; they may be completely irrelevant to happiness or how someone gets through their day. The point of these items is that they are unique quirks seen mostly in autistic people.

So ADOS does not tell you "severity" in the sense most people think of that word - it doesn't measure disability in daily life, distress experienced as a result of autistic traits, or anything of that nature. It's possible it tells you "degree of autisticness" in some sense, just sort of "how clear is it that this person is autistic vs. some other diagnosis." But someone (like my son) could have a high degree of "autisticness" without having what most would call "severe autism."

Disability or severity in common usage often relate to things that aren't autism itself: intellectual disability, anxiety, medical conditions, apraxia, etc. All of these things tend to occur with autism, and in a particular person may arise from the same cause or condition that also creates autistic traits. But ID or anxiety or whatever aren't directly measured by the ADOS, even though they may matter more than the autism diagnosis in determining what supports a person needs.

A good evaluation should include other assessments to figure out struggles in daily living, language, intelligence, sensory issues, motor skills, etc

Side note, there are a number of research papers out there using ADOS as an outcome measure (did the treatment lower ADOS score?), and this is flawed, since ADOS items may not be relevant to someone's actual happiness or life outcome. ADOS wasn't designed to be an outcome measure.

This use of ADOS in research may be one source of harmful autism therapy goals: focusing on stamping out autism's distinguishing features rather than on improving daily life for a person and their family.

Another ADOS factoid: scores drop as kids age. So if a person is in the lower end of the age range for a module you'd expect a higher score.