The finding of some the missing episodes of Doctor Who was the main subject for the last week: in 1980, over half of Doctor Who’s first 253 episodes were missing from the BBC’s archives and now there are only 97 of the not recovered. Yet.
The main reason for that horror is that the original 1960s material was erased and the tapes were re-recorded. There were several reason for the wiping of Doctor Who (and many other 1960s TV series), and they are explained in this article from DoctorWho.tv (with more details).
On Doctor Who, an episode would be recorded directly to videotape from studio, with as much of the work we would now term “post production” occurring at the same time. This meant music, location filming, the titles and credits, and model or effects shots were pre-recorded and played-in to the studio recording. Bar some small edits, this was essentially a finished programme.The videotape version was transmitted on the BBC, often after a very short period of time – as little as two or three weeks post-recording.
Most tapes were then sent to BBC Enterprises (the corporation’s commercial arm, now BBC Worldwide) for “telerecording” onto film – a much more durable and commonly-used medium – to be sold to international broadcasters.
Once both a UK transmission had occurred and an overseas sales film copy had been created, if neither Enterprises nor the BBC had any further interest in the episodes, the original videotapes were cleared for wiping.
Further more, an infographic was posted with some dates about Doctor Who episodes being returned from various areas of Earth.
The video is a segment from The One Show (October 11th, 2013) looking at the recovery of missing Doctor Who episodes. Presented by Peter Purves.