It's not straightforward because, as you raise, it's not completely clearly defined, and the OP was long and complex so a lot of opportunity for many possible points of view?
I guess I'm thinking of it as a journey from ignorance about one's nature to deliberately taking action to come to a better understanding. How that may happen is usually a journey events that trigger something to question oneself, mostly relative to others, and seek an explanation; be it for whatever reason, each can be a valid as the other - even just for one's own knowledge can be an important thing, all the other factors unlocked by a formal diagnosis such as therapies and benefits are another side to it.
To my mind, just to have that thought that there's something in your life you can't explain or rationalise that you wish to change, or even just understand, is the starting point of being assessed that may lead to formal diagnosis or not. For some it's the start of a self assessment and given the poor professional understanding currently, who's to say that can't be as accurate as a formal one? (though it won't get you any benefits etc).
So yes, I guess it's easy to quibble over the nuance of definitions (hell! I
love quibbling over definitions!
).
Yup, that's how I understood it, a number of years ago there was just the mental health diagnosis, it was and still is stimgatising to have at school.
I remember the few poor souls at school who were labelled as 'different' in some educational/social fashion, and if I thought myself excluded because I was 'shy', that was nothing to what they were put through back then. In those days even a relatively common physical ailment or disability could be enough to be socially excluded.