By 1939 it was too late for the journal editors to say anything, but they no longer had the luxury of not caring.

The way it seems to work is, it's always too early to say something, and then it's too late. It's never the "right time."

In "The Making of the Atomic Bomb" book it was clear that the physicists knew what was going on, and a lot had left by 1939. They wound up in Los Alamos.