42 C.F.R. § 21.46
Each board appointed pursuant to § 21.30 to consider the qualifications of candidates for appointment as officers shall assign a numerical rating to each candidate for appointment in the Regular Corps who passes the examination, and shall submit a report to the Surgeon General of the ratings and the relative standing of all such candidates for each grade in each profession or specialty within a profession. The Surgeon General shall submit each such report with his recommendations to the Secretary, and, if approved by the Secretary, the report shall constitute a merit roll from which the Secretary shall, in accordance with relative standing, recommend available persons to the President for nomination as commissioned officers of the Regular Corps. A board may consider any newly discovered evidence relating to the physical, professional, or personal qualifications of any candidate examined for appointment. Upon recommendation of such board after review of such evidence, the Surgeon General, with the approval of the Secretary, may correct the rating of a candidate or may qualify or disqualify a candidate. The placing of a candidate's name on a merit roll shall give no assurance of an appointment. A merit roll shall expire when a new merit roll in the same profession or specialty within a profession and grade has been established, but no merit roll shall continue in effect longer than two years after its approval by the Secretary. Every candidate who has not been nominated by the President for appointment prior to the expiration of a merit roll on which his name appears, shall, unless he requests the opportunity to be reexamined, be rated with the next group of candidates of the same profession or specialty within a profession for appointment in the same grade and shall be given the same rating he had on the expired merit roll. If two candidates who were examined at the same time receive the same numerical rating the elder candidate shall assume relative standing on the merit roll over the younger candidate. If a candidate whose name is being transferred from an expired to a new merit roll has the same numerical rating as a candidate whose name is being placed on the new merit roll for the first time, the former shall assume relative standing on the merit roll over the latter. The name of a candidate may be removed from a merit roll in the event that he refuses an appointment when offered. No candidate's eligibility for appointment shall exceed two years unless he again becomes eligible as the result of another examination.
42 C.F.R. §21.46