I'm dealing with depreciation on a coop used as a  commercial property that was inherited in 2014 and depreciation was never taken.  How far back can a 481(a) adjustment go? 

Is it just "open" years (in this case 2018-2020).  I see in the discussions that 2 years was mentioned but for 2021 seems like you could go back to 2018.

Would be happy just taking the adjustment in 2021, rather than filing 3 1040X forms.  But need to know how much can be taken.

Thanks