It sounds like archivists could image the disks and transport those across mediums, in the interest of archival, as long as they didn't distribute them, though. Am I mistaken?
Night of the Living Dead failed to ever have copyright protection due to lack of a copyright notice or registration, not from a need for renewal. Renewal became automatic in 1964, and registration or notice became optional in 1989. (And in 1976 it became possible to register for up to 5 years after publication, to allow for fixing mistakes like with Night of the Living Dead.)
But once the copyright expires on the disks, they may then be redistributed?