Alignment is one of the most important things (probably Terry would say THE most important thing) in shooting the bow. When I attended Fred Asbell's class many years ago, he said the first thing he looked at when his shots began to spread out was whether he was pushing with his bow arm. I think when he says pushing with his bow arm, he probably means the same thing you mean when you say moving your bow arm shoulder in, because the objective in both cases is better upper body alignment. Every error has a distinctive symptom, and the symptom for weakening of the bow arm or losing good bone on bone shoulder alignment is a general spreading out of the shots, as opposed to misses in one particular direction. At least, that's what I look for first when it starts happening to me.