Many of them didn't manage, though, and with diagnosis and recognition they might have avoided having to learn life skills the hard way.
Alcoholism, drugs, marriages filled with domestic abuse/servitude, living in squalid social housing with worsening mental health issues, being bullied at work/in the community, social ostracism, being exploited by a sibling or relative they relied on for support, etc.
Susan Boyle might have muddled through OK, but with an early diagnosis she could have avoided so much persecution/bullying in her local community and being taken advantage of by her siblings (who used her as a free carer for her ill/dying mother). She could have been successful and happier in life with support, instead of being limited to living with her mother into old age and unable to pursue relationships/friendships she desperately wanted.
Spend some time on WrongPlanet.com and have a look for yourself. There are many miserable, isolated, broken ND people out there. 83% of autistics consider suicide or have reoccurring suicidal thoughts, and around 40-60% will make at least one attempt (according to UK charity Autistica). The rates are similarly high for ADHD.
Compare that to the rates in the general population and it's a frightening reality - life is harder for ND people, even those patronisingly dismissed as 'high functioning'. Of course those with high support needs must be prioritised, but th suicide rates (especially among ND women and girls) are HORRIFYING. ND adults make up around 40% of psychiatric admissions.
All ND people are inherently vulnerable in one or two areas, even if successful. Temple Grandin, the most famous autistic person in America, is in her 60s now and has said she still relies on her elderly mother in many ways, though she has managed to hold down a fascinating engineering career and done a lot of autism related advocacy too.
We really can't ignore this or dismiss it with talk of building resilience. You can do that while also acknowledging there will always be a need for community support. The English are very bad at creating villages for each other, compared to African communities or European ones where children often live at home until marriage instead of being flung out at 18 and left to sink or swim. Neurodivergent children benefit from having structured support for longer than NTs. That's not mollycoddling, that's neurological reality.