Is any bill dated 28.03.2012 of Annual Maintenance Charges for period of 01.04.2012 to 31.03.2013 is a prior period expense if booked on 07/04/2012 i.e. FY 2012-13.
No it will not be treated as prior period item as the service will be provided in the year FY 2012-13. It can happen that the vendor has raised the bill in advance.
Just confirm that the period of service is mentioned on the bill.