For years, the original six seasons of Doctor have been incomplete, the result of a BBC archives purge in the early 70s. At the time, the BBC felt the value of repeating episodes from Doctor Who and other classic series was past and destroyed the episodes to free up storage space.
A few complete stories were retained an examples of an era and in some cases an individual episode of a story was kept. But for many years, the only way for fans to experience stories from the first six years was on the recollections of fans who saw them on their first run and the popular Target novelizations.
In the early 80s, a massive world-wide hunt began to track down any stories that may have been syndicated globally and restore them to the BBC archives. The result was that a good number of stories were returned, but there are still gaps where only a single episode or no episodes from a classic story exist. The BBC continues to search for stories and every once in a while an episode or two turns up or a few seconds of footage find their way back to the archives.
But never let it be said that just because the stories are gone that Doctor Who fans aren’t doing all they can to experience the stories. In the 60s, several fans set up reel to reel recorders near their television speakers and recorded the original soundtracks to the stories. The BBC also hired a photographer team to take images from each story called a TeleSnap for most of the lost stories. For years, fans traded audio copies of the story on cassette tapes with each other at conventions and later on the Internet. In the 90s, enterprising fans would marry the photos from the TeleSnaps with the audio to recreate “reconstructions” of lost stories.
Now, the concept of taking the original audio footage and marrying it to computer animated recreations is taking off again. A group of fans are looking to re-create the stories for the new modern audience and seems to be taking a cue from the work done for the DVD release of “The Invasion” last year. Clips and examples are available on a YouTube channel devoted to the recreation of the lost stories.
https://www.youtube.com/watch?v=HvFQw9SgA8k
As of publication, there has been no official response from the BBC to the fans recreating the old stories. However, in the past, the fan re-creations have come under fire if they are produced for a profit.