I think this requires fiduciary judgment. If you a find a participant or a participant finds you, at a minimum give that participant the notices that are currently relevant. I don't see a need to send the participant a 20-year old SAR, and I can't imagine the DOL or a court would ding you for that - assuming the plan acted in accordance with ERISA's fiduciary duties all those years. Of course, written requests would be a different matter. If you want to dot all your i's and cross all your t's and mitigate all risk, give the participant everything.