ASD is very dynamic. It is not linear spectrum, think of it more like a polar graph. I would think 67 may be enough people to get an idea for one "hallmark" but certainly not all of them as a comprehension.
Many ASD-related surveys are not confirmed-diagnosed either, but only self-reporting as ASD.
I mean I get it, it'd be a colossal pain to verify all that medical data, but it also makes for bad science.
If you self report as autistic, you're probably autistic. Especially because, in practice, an autistic person is defined as someone who self-reports autistic traits to a health care provider.
Self reporting autism can be surprisingly accurate.