I have a new CPA practice, (I have been auditing and accounting governmental and NFP for nearly 30 yrs), however I am now learning taxes and private industry. I also do CAS. I learned since I decided to prepare tax returns in 2020 that one of my client's in the construction industry who I do CAS for his business, that he filed as Head of Household for the last few years. However, he is and was married while he filed as Head of Household. 

My question is should I recommend he go back and amend this? I will not prepare his tax of course unless he agrees to comply. 

Thank you