@lg79 wrote:
.....should I go back and file a 3115 for change of accounting method and file amended returns for as far back as allowed?
You do not file amended returns; you only file Form 3115 for which professional guidance is recommended.
Once you file returns for two consecutive tax years without deducting depreciation, you cannot amend those prior returns; you used an impermissible accounting method that can only be corrected by filing Form 3115.
Adoption of accounting method defined.
Generally, you adopt a method of accounting for depreciation by using a permissible method of determining depreciation when you file your first tax return, or by using the same impermissible method of determining depreciation in two or more consecutively filed tax returns.
See https://www.irs.gov/publications/p946#en_US_2019_publink1000107385
