For an ERISA-governed retirement plan, a situation in which, without another valid beneficiary designation, the plan-provided default beneficiary is the personal representative of the decedent’s estate, the plan’s administrator decides what evidence persuades the administrator to approve a claim.
A State’s law might be relevant in, and might support, an administrator’s fact-finding and decision-making about who is or isn’t a personal representative, and about whether the plan’s obligation to pay the decedent’s personal representative has been satisfied.
Yet, the claims procedure and a fiduciary’s decision-making are governed by the documents governing the plan, including an ERISA § 503 claims procedure, and ERISA’s title I.
Many administrators look for “letters testamentary” or “letters of administration”, or some other court order that grants or recognize a person’s authority to act for the decedent’s estate. And some administrators use further steps designed to test whether what’s presented as such a record or certificate is authentic or a forgery.
Some administrators might act following a claimant’s small-estate affidavit if it meets the conditions under a relevant State’s law and meets any further conditions the plan or its administrator imposes. Other administrators do not consider a small-estate affidavit. (For a background, including views that might differ from some of my observations, see https://benefitslink.com/boards/topic/63408-does-a-plan-pay-on-a-small-estate-affidavit/.)
If a plan’s administrator has not already done so, it should design, with its ERISA lawyer’s advice, a procedure for these situations—a procedure the administrator is ready to apply regularly, uniformly, and impartially, with no more than prudent plan-administration expense.
An obedient and prudent fiduciary follows one’s claims procedure (except insofar as it’s contrary to ERISA’s title I or other Federal law).
This is not advice to anyone.