You should understand that your definition is out of date, but I'll respond:

> If somebody has coping strategies that effectively mask their autism (in the early childhood/developmental stage specifically), they DO NOT HAVE autism

The DSM V diagnoses autism much more broadly -- https://www.cdc.gov/ncbddd/autism/hcp-dsm.html -- and it's very plausible that a child might not be identified. (For example, my parents were drunkards, I was not assessed as a child.) A child might also learn that they are punished for some behaviors such as stimming, and learn not to do it publicly, but still engage in that behavior privately.

Autism diagnoses only require that person needs 'support', and explicitly calls out that symptoms may be masked by coping strategies.

> How SPECIFICALLY are these additional people getting diagnosed?

Psychologists and psychiatrists usually start with a series of screening questions, followed by several in person discussions sessions where they probe into both your own self perceptions and the perceptions of others.

There is a 2018 paper that specifically identifies camoflauging traits and a screener that can be used to help identify adults (and others) who have built systems to survive in the world. It's called the CAT-Q. See the paper: https://link.springer.com/article/10.1007/s10803-018-3792-6

> Is there special training diagnosticians get to unveil the secret masked signs of autism?

Yes. Typically a psych degree (doctorate) with an emphasis on ASD, but sometimes masters level mental health professionals working in concert with an MD.

> What are these scientific advances I've heard vaguely cited for the rise in autism diagnosis over the years?

Well, see the 2018 paper I linked above. If it would be helpful, there are many other papers from 2000 onward that specifically address everything from repetitive behaviors to social isolation to meltdowns, etc. Mostly, we've improved our screening processes, which means we've got better, more accurate criteria.

> Why is it even possible for a diagnostic criteria that hasn't changed to result in dramatically different diagnostic rates over time, doesn't that prove the diagnostic process is fundamentally unreliable and thus fundamentally scientifically invalid?

The DSM criteria have changed between DSM 4 and DSM 5, in 2013. The DSM used to separate Autism and Aspergers as categorically different, but they've removed the Asperger's category and adjusted the criteria for a diagnosis.

It's also important to remember that science is never stable. The point of science is to revise over time our criteria. The point is to evaluate what new information we have.

And observed rates have risen, from about 1% to about 2% over the past decade, which you've correctly identified, but you would expect that because screenings have improved, diagnosticians have evolved, and we've put more emphasis on testing people.

That's not a huge number of people, and it's fairly reasonable to assume that as we've developed the science, we're catching people who previously would have been missed by less accurate tests.

It could also be that whatever causes autism is also happening more. There's a whole lot of factors, but no, that doesn't mean the science is bad it just means we haven't answered all the questions we have yet.

> The fundamental cause of the rise of Autism is that both schools and parents both financially benefit from a child being labelled as "Autistic"

That's a pretty conspiratorial claim for an increase in diagnoses that can adequately be explained by "we're better at testing for it now."

> It's driven by parents and schools looking for money, money is the dynamo driving this, autistics are rainmakers.

This is likewise a conspiratorial claim. Can you provide evidence of this? Because "I've seen it" is at best anecdotal, and runs counter to the prevailing idea that being labelled as autistic by the medical community can deny you agency in academic, medical, and social contexts.