According to Baseball-Reference.com Heilmann did indeed hit .531 by May 1st, but they only played 13 games in April 1923.
But by June 1st he was hitting .419, not .430 and certainly not .526.
Hitting .419 on June 1st versus hitting .526 on June 1st is pretty far off in my book.
Maybe baseball-reference.com has the figures wrong.
According to them, by August 1st, he was hitting .392, finishing at .398