I don't know a lot about lost media, so I only added a few notorious examples that I've heard of. I'd like people to add responses of lost media that they find interesting. Please make your responses as specific and unambiguous as possible.

I will resolve options as YES only if the material is not only found, but also made available publicly.

If parts of a piece of media are found (e. g. half of a Doctor Who episode) I'll resolve to a percentage. I will not count finds that are not the actual media form that people are looking for (i. e. stills of a movie instead of footage, sheet music to a lost song instead of the original recording etc.). I will count finds that are of lower quality than the original (e. g. a screen recording). These will resolve as YES, not to a percentage.

If there's any ambiguity about whether the media found is not the real thing, I'll see what the consensus on Wikipedia and the /r/lostmedia subreddit is.