With me, it's a little complicated LOL
I was diagnosed, by a professional, with Infantile Autism when I was three. This was because I did not speak. And because I was oblivious to the world around me. It was a valid diagnosis for my functioning at the time. Infantile Autism carried a poor prognosis in those days.
Then I was diagnosed with Brain Damage/Injury (a frequent diagnosis, in my opinion, for many who would be diagnosed with HFA/Asperger's today), when I was about four. This diagnosis was seemingly less serious, the prognosis was better, and was based upon improvements I made in my functioning, like acquiring speech at age 5 1/2, and presenting more Aspergian than classis autistic. Later on, this diagnosis was called Minimal Brain Dysfunction. I went to a Brain-Injured nursery school.
I did not think of myself as having autism when I was a child, even after I learned about it when I was nine. I thought of myself as weird, and supposedly cured of my so-called retardation via brain surgery. My friend's brother had (and has) what would now be called Level 3 autism. He is non-verbal, yet has self-care skills. I thought of HIM as being autistic.
Then along came Asperger's Syndrome, and the notion of the Autistic Spectrum around the early 1990s. There existed a vague notion of a "high-functioning' form of autism in the 1980s, though it wasn't official until the DSM IV.
When I read about Asperger's Syndrome, I realized that it fit me to a tee, despite the fact of my speech delay.
Thus, I self-diagnosed myself as being on the Spectrum. Not exactly Asperger's because of the speech delay. More like classic autism because of the history. Then, in 2014, I got on Wrong Planet. The rest is history.