"[According to Rev. Rul. 2019-19,] a check that was distributed and received by the payee so he or she could cash the check in the year issued is taxable income to the participant (or beneficiary) and subject to Form 1099-R reporting and withholding rules. This answer does not vary regardless of whether the participant or beneficiary keeps the uncashed check, sends it back to the plan, destroys it, or cashes it in a subsequent year."  MORE >>