Your comment doesn’t address my question of how many people are misclassified by IQ test. I suspect smart people with high functioning autism and the like are not accurately measured. Not saying any of this applies to Feynman by the way. Just used him as an example of where an IQ exam underestimated someone.

It´s fairly well known that people from impoverished backgrounds get lower grades for several reasons - not ever having practiced similar questions and vocabulary issues: there have been some quite notorious questions, especially over in England that were dependent on different social classes having different vocabularies, etc.