Back when the problem was too much psychiatric care instead of not enough there was this famous experiment

https://en.wikipedia.org/wiki/Rosenhan_experiment

This one is more positive but is checking that different diagnosticians get the same answer

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5980511/

and if that was applied to the "Thud" experiment you'd have poor diagnosis with a very high kappa (interrater agreement)