Comment by WalterBright
15 hours ago
> there is at least one tape that we know used to have Doctor Who on it but which now has another programme.
Recording over another recording does not completely erase the other. I wonder if it could be recovered.
I worked in a broadcast company archive (doing database work). Tapes were often reused. Fragments of previous recordings -- sometimes just a few frames, occasionally many minutes -- may remain at the beginning or end of the tape. AFAIK tapes were never completely erased before recording over top.
I was invloed in a digitisation project, the scanning companies were instructed to process the whole tape in case there were fragments of older programs at the end. A 30 minute tape may have 15 minutes of program, then a period of blank/black, then the remains of an older program for several minutes after that.
It has been suggested numerous times, but the BBC didn’t just record over the top - the tapes were erased with a degausser before reuse.
Someone at the BBC with a degausser yelling "Exterminate! Exterminate!"
Oh well.