There was probably a renaissance period when conversion equipment was being actively developed and available, but that time is probably gone. For example I think a good film scanner would be the Nikon Super Coolscan 8000 ED, but current state of the art falls far short. For film, vcr tapes and more we should be doing so much better.

I have old family super-8 films that are kind of convertible, but not the magnetic sound strip.

Lost Doctor Who episodes are one of them. Dad's Army also has lost black and white episodes (the colour ones have been repeated ad nauseam all my lifetime).

I can think of a few others. Scotch on the Rocks was a political hit piece written by Douglas Hurd showing an armed Scottish uprising along the lines of Northern Ireland. It was supposed to frighten people away from Scottish nationalism, but ended up causing copycat incidents. It vanished shortly after being broadcast probably because of its unintended effects.

The ultimate would be some of the pre-WW2 television broadcasts. Most of these were broadcast in the London area and practically nowhere else. Almost no one had recording equipment back then and they were often broadcast live.

wrong doctor