Since the establishment of an archival policy for television in 1978, BBC archivists and others over the years have used various contacts in the UK and abroad to try to track down missing programmes. For example, all BBC Worldwide customers—broadcasters around the world—who had bought programmes from the corporation were contacted to see if they still had copies which could be returned; "Doctor Who" is a prime example of how this method recovered episodes that the corporation did not hold itself. At the turn of the 21st century, the BBC established its Archive Treasure Hunt, a public appeal to recover lost productions, which has had some successes.