My Dad was, and so is bamaboy, but I was spared that afflicition.
Dad shot off his right shoulder, left I dominant, and it gave him fits. He was a rather poor wing shot, and missed quite a bit w/ a rifle as well. If he had time to set up and get "prepared" he did OK w/ a rifle. When things happened fast, he did not do so well. Dad didn't have a clue about his cross dominance till he was in his 50's, and he never tried changing even after it was diagnosed.
I spotted it early on w/ bamaboy and got him shooting off his left shoulder/left eye (there's no doubt he's right handed) right off, and the kid does really well. With a handgun he shoots right handed and just lines up with the left eye w/o any trouble.