Marcone will have taken up the shadow and got it to show him its worth, but probably waited years to take up the coin.
The host can influence the shadow as Harry/Lash proved. Harry was the only previous host not to quickly have the coin fully taken up and the shadow rejoin with the Angel. This rejoining never happened with Harry, due to Lash’s sacrifice, but if Marcone had the Coin for years he was working on the Namshiel all that time with his considerable will. When he finally took it up Namshiel will have had a much changed shadow returned to him, changing him in a way which has not previously occurred, and one not expected
Marcone deliberately and purposefully corrupted a Fallen Angel as an exercise of Free Will. I think he has been successful.
If someone like Michael or Father Forthill took up a shadow and held it for years and then took up the Coin could this lead to a redemption of the Denarian? The ultimate purpose of the Knights of the Sword is to redeem those who who have taken up the coin, like Sanya. What is they can redeem via the shadows the Angel?
The next host for the shadow of Anduriel (Master of Shadows)will be Michael, when he persuades Nicky, sans his tie to drop his coin. That is a reason to for Jim keep Michael alive.his purpose is NOT complete.