Inventory the periods before naming a completion date
List the years under discussion and mark what return information, source statements, and filing evidence is available for each. A missing return copy and an unfiled return are not necessarily the same situation; retain the evidence needed to clarify the status. Consult current IRS information about past-due returns and ask what requirements apply to the actual taxpayer or entity.
Plan the document work without inventing progress
For each missing record, identify a legitimate source and a retrieval step. Keep reconstructed figures and their limitations visible for review. Separate collecting papers from preparing, signing, filing, and addressing a resulting amount. If professional help is proposed, clarify the covered periods, authorization, and responsibility for submission evidence. Save the final supplied or filed version alongside confirmation. A project plan is useful because it describes the remaining work; it cannot certify filing status, calculate a liability, or promise that an account consequence will disappear.