I self-diagnosed Aspergers in the mid 2000s. The primarily inattentive subtype of ADHD is a better match for my symptoms, particularly the social ones, but both my psychiatrist and neuropsychologist agreed that my self-diagnosis made sense and I have traits of both disorders. They are very often comorbid. I just wasn't familiar enough with the diagnostic criteria of ADHD to realize I had it. (A roommate with ADHD that I had at the time suggested it, though.)

Also, ADHD is in fact under-diagnosed, particularly in adults and especially in women.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4195639/

Some children are overmedicated, but there's evidence it's also underdiagnosed in children.