I am part of the SMPY study cohort (from 1982) and have another close friend who is from the 1983 or 1984 study cohort. (The qualification at the time was 700 or greater on the SAT Math before age 13. This was, of course "SAT one" scoring system.)

I also spent some in summer camps with other students in the study and have remained casual friends with some of them over the years. I don't see any evidence to suggest that that level of demonstrated ability is transient.