Given that the term autism didn't exist before 1911 it probably wasn't being diagnosed a whole lot before then. But I would guess it went up as understanding and awareness of it grew, but there were definitely descriptions of people who met the criteria for it long before then.
Seeing the raw numbers is impactful and I would also like to see these figures as percentages of the whole since they're comparing different times with different populations.
Would be neat to see deaths or hospitalizations pre/post visualized this way too to really drive home the point for the “measles weren’t really that bad” crowd.