I've never been formally diagnosed, but I'm pretty sure that I am on the spectrum. Even DW, who has a First in psychology and was initially sceptical, has come to think that too.
I've been very successful by many standards, but there's always a degree of retrospective regret about what I might have achieved had it been recognised and I had had appropriate support. But, and it's a big but, when I was a child autistic people were non-verbal, (apparently) intellectually very deficient and only able to live in institutions. Having ASD/ADD/ADHD and being 'high-functioning' simply wasn't recognised.
I also had a lifetime's worth of digestive issues and only got diagnosed as coeliac at 60. Again, when I was young only severe and classic cases were recognised, but applying current knowledge shows that I was suffering all my life. The same applies to my asthma, which was tentatively recognised in my 40s and only properly diagnosed at 55.
And I strongly suspect I have something else lifelong too but it's more socially problematic even than ASD.
Ultimately, hindsight is a wonderful thing, but just as I didn't choose my parents, or siblings, or schools, or children, or mid-career redundancy I didn't choose the non- and mis-diagnoses, and like anyone my age I've got a long list of decisions that seemed good at the time but less so later on (eg when I left a bad job for one that turned out to be worse, would I have been better with sticking with the bad one, and working hard to get promoted to a better position, or was the really bad job a blessing in disguise as it pushed me to make a bigger change for the better, without which I wouldn't have met DW?). I've come to the view that grieving about the past is the enemy of a happier better life in the future.