Usually IT 0585,0586 does not allow to enter values for previous year which is standard approach but your saying you are entering for last payroll period where how system behaves is you can enter the values from 01.04.2014 - 31.03.2015 if you try to enter 01.04.2013 - 31.03.2014 then system does not allow you to create or modify for previous years.
Regards
Venkatesh
