Build a short year-by-year status list
For each affected year, record whether a return was filed, whether it was assessed and whether a change request is pending. Keep the return copy, assessment and submission evidence where available. The same taxpayer can have different issues in different years.
Identify the source of the newly found information. A missed income slip, incomplete business record and an assessment dispute do not automatically follow the same route. Older-year limits and any separate objection deadlines should be checked promptly.
Worked example: two years, two actions
Suppose a hypothetical Ottawa resident has an unfiled 2024 return with $48,800 of documented employment income. Their assessed 2025 return already reports $54,000, but an $820 interest slip was omitted. The 2024 issue requires its own return preparation; the 2025 review considers a supported adjustment.
If the $820 is confirmed as additional reportable 2025 interest, the income-source total under review becomes $54,820 before other items. It does not belong in the missing 2024 return or the future 2026 return merely because it was discovered today.
Keep filing deadlines separate from payments
The ordinary 2025 filing and payment deadline was April 30, 2026. For the usual self-employed circumstances, filing was due June 15 while payment remained April 30. Both dates are already past as of September 6, 2026. Preparing the paperwork later does not create a new original deadline.
A payment does not file a return, and filing does not establish that a payment reached the intended account. Track those actions separately. Interest, penalties, relief or disclosure questions require their own review instead of an assumption that reconstruction removes prior consequences.
Retain evidence through the final result
CRA requires a notice of assessment before a change request. If another change is pending, wait for its response before requesting further changes under the ordinary guidance. Confirm eligibility for the proposed online or paper correction route and the necessary authorization.
Save the agreed figures, supporting records and submission confirmation. Compare the later assessment or reassessment with the work completed. That closing step explains whether the intended correction was processed and identifies any remaining issue without sending duplicate returns or overlapping requests.
Put this into practice
Sources and current guidance
A practical next step
Bring the records you have.
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