During the fight in the bar, William knocks the gun to the ground & it comes to rest against a chair leg. When he dives for the gun it is no longer against the chair. As he tucks the gun into his waistband another gun can be seen on the floor several inches away from the chair.
At the beginning of season 4 Duke finds that Nathan is no longer with the HPD and has been using his trouble to make money. He finds him outside of a diner surrounded by bikers who pay him to take punches (as he doesn't feel them). Nathan has a beard that has grown out in the six months that Duke has been gone. When Duke confronts Nathan, the scene cuts. When the scene reopens, Nathan is back to his stubble face.