Authentication of supply invoices: central excise endorsement required for deemed export benefits; registered recipients must notify and allow verification. For claiming deemed export benefits, registered recipient units must notify the jurisdictional Superintendent of Central Excise, obtain a dated acknowledgement, and permit physical verification within five working days; if invoice details match, the Superintendent shall endorse the invoice or statement immediately but not later than twenty one days from the date of supply or receipt of intimation. Unregistered recipients may provide a certificate from a Chartered Accountant or Chartered Engineer; Central Excise officers need not issue certificates in such cases.