From what I've seen, there are -probably- around a hundred mental types in the social strata I spend most of my time in, maybe two hundred on the high end. I'd hazard a guess that there are probably five hundred to a thousand mental types overall. I've encountered only a handful - four or five - minds I've not seen repeated, which I internally translate to "exceptionally rare". I've met exactly one person whose mind was remotely similar to my own; they had suffered brain damage, and I didn't know the person before to ascertain whether or not the similarity was a result of the brain damage or not.