The NSA has a video recording of a 1982 lecture by Adm. Grace Hopper titled “Future Possibilities: Data, Hardware, Software, and People.” The agency is (so far) refusing to release it.
Basically, the recording is in an obscure video format. People at the NSA can’t easily watch it, so they can’t redact it. So they won’t do anything.
The simple/charitable explanation might be that they don’t necessarily expect there to be anything that still needs to be redacted, but they won’t release it until they’re sure.