The series suffered from the BBC's lack of a proper archiving policy until 1978. It was BBC policy before 1978 to wipe master tapes and reuse them for other programmes, hence saving money and storage space. The total number of editions known to exist on film or videotape stands at twenty (and a half) out of 49. Additionally, visual excerpts from eight episodes are held, plus various off-air audio sequences from 16 installments.