Estimated from the value ranges in their annual financial disclosures; the filings give ranges, not exact figures.
Track record
Buys of one stock within six months count once, from the first buy. Each is measured over the next 120 trading days (about 6 months), beside the S&P 500 over the same days. A fact about the stocks, not money anyone made.
One buy is old enough to measure: too few to compare with the S&P 500.