Duplicate invoice check

Hi experts,

Presently i configured duplicate invoice check for miro .Now system checks these parameters.

Vendor

Currency

Company code

Gross invoice amount

Reference document number

Invoice date.

& if repeat same reference number it create error massage. But suppose i put reference number 1212 with document date 31-07-2013

& for second document suppose i enter reference number 1212 with the date 01-08-2013 system allow to post invoice. So query is suppose date is different but reference number is same ,system should restrict to post invoice.Please help to achieve this.

Regards

ragini