I did my son's 2019 tax return last year and didn't realize that he had paid state income tax when he worked in Delaware for a school internship. My question is, I am going to file his 2020 federal and state tax returns this week and wanted to know if I could file his 2019 state return at a later date. I did a draft version of his 2019 state return and he is owed a refund. Thanks.
