No, just hit it now - it's already hard.
Without some super fast oil or brine, if you heated it up to critical - which is about 1500 degrees, and then cooed it off, it would go dead soft.
And no, you don't know that the first two would make good files, the newer they are, the more suspect they would be. Seems industry has found more ways to only surface harden steels and such these days which makes the older files better - in my opinion.