For the purposes of sections 1702-1704 of this title any finding, report, or record, or duly certified copy thereof, purporting to have been signed by such an officer or employee of the United States as is described in section 1702 of this title, shall prima facie be deemed to have been signed and issued by such an officer or employee pursuant to law, and the person signing same shall prima facie be deemed to have acted within the scope of his or her authority. If a copy purports to have been certified by a person authorized by law to certify the same, such certified copy shall be prima facie evidence of his or her authority so to certify.