@MrsSunshine2b nursery starting age is 3. So one year off. In some areas, even if you raised concerns at birth, you'd still be on the waiting list or only just seen at age 3.
Are you actually familiar with any of this stuff or are you just making stuff up as you go along to suit your own narrative?
You can have a completely non verbal, incontinent, self harming , putting everything in his mouth child at 3 or 4 and still no diagnosis until a year later. Can you see it? Yes. Can you prove it with a letter from the consultant? No.
I actually work in a school. In preschool (2 and a half yos) about 3/4 are in nappies/pull ups but being toilet trained. In nursery (3/4 yos) 99% of the children are in pants but do have quite frequent accidents (hell, I've had y6's having accidents) , in reception(5 yos) 99% of the children are fully toilet trained with the occasional accident. We do have 6 children in nappies, all bar one exactly how I described. The one that isn't (only 4 though) is making some progress and the parents are fully cooperative and supportive and putting the work in, we just add to it. All on the waiting list for SEN schools and one is now nearly 7 (still non verbal, still incontinent, mum and us fighting like fuck to get him a place and the support he actually needs).