When advancing your fiscal year or calendar year, it is important to create a backup. This should be named something that refers to the year end date or calendar year. The location should also be noted and saved in a safe place for future use. An example would be is if you needed these previous backups due to the CRA auditing the company and requesting payroll information (or invoices) beyond 2 years of your present file. Restoring from an old backup will allow reports to be viewed of the previous year and opened year in question.
Refer to Kb 10390 "How do I create a backup?"