I don't believe cases where changing your strategy in a non-equilibrium state are considered, as the assumption that no other player will shift their own strate

I don't believe cases where changing your strategy in a non-equilibrium state are considered, as the assumption that no other player will shift their own strategy will not hold. Otherwise, you might as well consider the case P1 always chooses 1, P2 always chooses 1 and P3 always chooses 2.