Diagnosis is now much better, there’s still a very long way to go as the system does still need improving.
It’s something that can be hard to ‘get’ my son has SEN, he is hearing impaired, however with aids his hearing is good and it has so far had zero impact on his ability to communicate, in fact he’s verbally bilingual. But of course hearing aids are visible.
He is adopted which of course comes with challenges, this is his ‘invisible’ need. People can see he has a hearing impairment, they can’t see attachment issues, food anxiety or the many random things that lead to fight/flight/freeze.
He is very bright, he turns five in June, he can do simple addition and subtraction, he is a good reader and shows good reading comprehension, his verbal ability is also very good.
What I have noticed is the number of people who think having additional needs means the child/person lacks intelligence. Yes some additional needs do mean someone may have a slightly lower IQ, but that seems to be the automatic thinking for some people.
Where children are concerned people will sometimes say things like “well he’s okay now” yeah he’s definitely okay and has no ill effects from being used as an ashtray, or being force fed a dirty nappy 
Generally society is getting better at understanding additional needs, but there is still a very long way to go. Another big problem is that until recently if a child had additional needs putting them in an institution and forgetting about them was a viable option, there is still societal shame surrounding additional needs.
Ideally more people would research ACEs and the impact it can have for someones entire life.