CRA’s voluntary disclosure practice is to go back only to years for which there is supporting documentation, and no earlier

Although a voluntary disclosure must generally be of information that is at least one year overdue (in order to prevent use of voluntary disclosures to avoid late-filing penalties), where returns for multiple GST reporting periods have not been filed and any one of the returns is more than one year past due, the entire series of returns will be eligible for voluntary disclosure.

Although CRA can go back more than four years where there has been a neglectful misrepresentation etc., “in practice, however, the CRA will (by administrative largesse) only include reporting periods for which supporting documentation is available in the disclosure.”

Neal Armstrong. Summary of Ryan Rabinovitch, Angelo Discepola, "Solving Sales Tax Non-compliance Through the Canadian Voluntary Disclosure Program," Tax Litigation (Federated Press), Vol. XIX, No. 4, 2015, p. 1175 under ETA s. 281.1(1).