5 CFR § 831.103 - Evidence.

(a) Standard Form 2806 (Individual Retirement Record) is the basic record for action on all claims for annuity or refund, and those pertaining to deceased employees, deceased Members, or deceased annuitants.

(b) When the records of the department or agency concerned are lost, destroyed, or incomplete, the department or agency shall request the General Accounting Office, through OPM, to furnish the data that it considers necessary for a proper determination of the rights of the claimant. When an official record cannot develop the required information, the department, agency, or OPM should request inferior or secondary evidence which is then admissible.