I have a 2020 Individual Income tax Return with an NOL. The year 2019 had Taxable Income, but the year 2018 did not. Taxpayer was given a proper 1045, but mailed it late and lost the privilege of  being able to use it.

Now, our only option is a 1040X. My question is do we have to file a 1040X for 2018proper years to file, Federal Forms, 2019, and 2020 or just for the year 2020 that would include the other 2 years or is this a special year and we must go back 5 years using a 1040X.