20 CFR § 219.33 - Evidence of a deemed valid marriage.
(a) Preferred evidence. Preferred evidence of a deemed valid marriage is—
(1) Evidence of a ceremonial marriage as described in § 219.31;
(2) If both the employee and spouse are alive, the spouse's signed statement that he or she went through the ceremony in good faith and his or her reasons for believing the marriage was valid; or if the employee is dead, the widow or widower's signed statement to that effect;
(3) If required to remove a reasonable doubt, the signed statements of other persons who have information about what the parties knew about any previous marriage or other facts showing whether the parties went through the marriage ceremony in good faith; and
(4) Evidence that the parties were living in the same household when the employee applied for payments; or, if the employee is dead, when he or she died. See § 219.51 for the evidence required to demonstrate living in the same household.
(b) Other evidence of a deemed valid marriage. If preferred evidence of a deemed valid marriage cannot be obtained, the claimant must explain the reason therefor and submit other convincing evidence of the marriage.