amended returns where a refund is due can only be filed for 2017 forward. correction of this depreciation error for 9 years, if needed, will require filing form 3115. I suggest you use a pro. it is in your best interest to file for this relief if needed. you may have taken no depreciation for 9 years but the IRS rules say when you sell depreciable property you must take into account the larger of depreciation allowed (might be 0 in your situation) or the amount that would have been allowed if depreciation was computed correctly. so the basis of your property for computing gain/loss would be reduced by 9 years of phantom depreciation.
