I am doing someone's taxes and their husband passed away. I did 2018, 2019, 2020, and 2021, The husband did not pass away until 2021. Do I only do the 1310 for 2021 or do I have to do it for the past years as well? 

We also have to mail it in. Should the wife sign his name for 2018, 2019, and 2020 being mailed in?