Processing Arrears in Retroactive Accounting 
Processing Arrears in Retroactive Accounting
Use
When the original payroll is run for a payroll period, deduction wage types are subtracted and paid. This procedure cannot be reversed. If you have to trigger retroactive accounting in this payroll period after you have changed a deductions wage type, then the deduction wage type is processed specially.
Features
The changed amount of the deduction wage type cannot be taken into consideration by the system. In retroactive accounting the amount of the deductions wage type that was processed in the original run is processed again.
Of course, a positive or negative difference can exist between the deduction amount in the original system and the changed deduction amount. This difference can be written to the next payroll period using the Arrears table (ARRRS).
In Customizing for Payroll under Deductions®Arrears and Priorities ®
Maintain Arrears Deductions for Retroactive Accounting you determine how changed deduction wage types should be processed in retroactive accounting. 
In retroactive accounting arrears are processed in a different way to that of an original period. Processing in retroactive accounting takes place in function PRDNT, namely before the tax calculation. The loop must therefore be performed again, there is no iteration. Processing in functions PRPRI and PREND does not take place either.