Complex sentence: Most of the show's 26 episodes from series 1-3 that were videotaped in black and white no longer exist; they were wiped by the BBC during the early 1970s.
Split into simpler sentences: Most of the show's 26 episodes from series 1-3 that were videotaped in black and white hardly exist. They were wiped by the BBC during the early 1970s.