A court decree of annulment holds that there was no valid marriage ever existed. Taxpayers who have secured an annulment are now considered unmarried for the entire period that the marriage purportedly existed.
It makes sense that the couple initially filed tax returns for that period as married filing jointly or married filing separately. Assuming they filed taxes.
Since the marriage now never existed they are required to file amended returns using “Single” or if qualified “Head of Household” filing status.
It seems that the fun never ends with the major modification of one’s life.