Bob naviaux says there has been a definite increase since the 80s be ause of the 5,000 plus new chemicals put into the food chain and environment without proper study. Plastics alone are a massive endocrine disruptor.
Naviaux calls this " ECOGENIC" autism. In other words the environment is causing the changes. He cites vaccines amongst some of the things that stop our healing processes working properly.
He did proof of concept trials with a drug called suramin. They helped the autistic kids.
So this is not down purely to better recognition although of course that plays a part too.
I believe naviaux works for NASA now. He's a bonifued authority on autism and mitochondrial health