To “insert” a payroll into a prior period, use the after-the-fact payroll feature. That is, you can start a new pay period with a Year or Year/Month that precedes that of the latest processed pay period Year/Month.
If no other checks have been posted in the current pay period, you can specify a check date whose Year and Month precede that of the latest processed pay period Year/Month.
As long as the Year/Month and/or date does not fall within a quarter which has been closed using Payroll/Quarterly Checklist, you can post to a Year/Month which precedes that of the latest processed pay period.
Process the payroll and close the period. Give it a meaningful name. For example, if the pay period contains checks for a period named 2015.02.27, give this pay period the name 2015.02.27a.
Go to Payroll/After the Fact Payroll
Note: Use the Payroll/Prior Year Adjustments window to correct Payroll year-to-date information accumulated during the prior year after you have started running Payrolls in the new year. The command is dimmed (not available) unless you have opened the first pay period in Quarter 1 of the new year.