Doctor Who
Before 1978, the BBC would sometimes throw away or wipe episodes they did not need. This was because they did not usually show episodes on television more than once, and they needed to reuse video tape to record new broadcasts. Some of the episodes that were thrown away have been found since then, but 97 of the 851 episodes are still missing. However, audio recordings of all missing episodes exist, and some of these have been released on home video with animations.