Inspector Sharpe, who appears in Agatha Christie's Hickory Dickory Dock, replaces Inspector Japp on cases for this series due to the surname sounding like an anti-Japanese racial slur.
Miss Marple's great-niece, Mabel West, is non-canonical character created for the series. Her father Raymond West (Miss Marple's nephew) does appear in numerous Marple stories, but in the books he is father to two sons. However, the name Mabel does appear in connection to Miss Marple's family; her niece Mable Denman (Raymond's cousin) is accused of murder in The Thirteen Problems.