Price Issue of Subcontracting material

Dear SAP Experts,

I a m facing an rissue. When we un cost estimation for a particular material of Subcontracting, system is taking old PO in cost estimation run through t-code ck11n. We have created number of PO after that one. System is only considering PO for a specific Vendor. This issue is only for couple of materials.  Kindly guide me how to resolve this issue.

Thanks

Muhammad Umar