It depends. You will need to report the participant information in Part III of the Form 8955-SSA using Code D if they were previously reported by you as a separated participant with deferred vested benefits.
Also, you would need to report a participant that had commenced receiving benefits if that participant later becomes a deferred vested participant. For example, a separated participant who has been receiving benefits stops receiving benefits, but is still entitled to a deferred vested benefit under the plan. Thus, the separated participant becomes a deferred vested participant and should be reported on Form 8955-SSA using Code A.