My client recently learned that his x-wife failed to file a joint return in 2020. They were estranged at the time but were working things out or so he thought. According to him, he provided her with his w-2 and assumed that she had filed the taxes as they always had done jointly. He recently learned that his 2020 return has not been filed. I'm working on the return and would like to know if I should use his current address and locality code or where he resided in 2020.