Complex sentence: There are currently a number of DVDs available which contain all series; even though it is advertised as complete series 1--4 it is missing the episode snow business, although the episode of series 2 snow business is on a separate DVD.
Split into simpler sentences: There are currently a number of DVDs available which contain all series. Even though it is advertised as complete, the series 1--4 DVD set is missing the episode "Snow Business," although the episode of series two "Snow Business" is on a separate DVD.