Well, first off, "people" you're right.
Judi Dench was never in "She Fell Among Thieves."
BUT "She Fell Among Thieves" was part of a series in the UK known as the "BBC 2 Play of the Week" just like the play that Judi WAS in...which was called "On Giant's Shoulders" and in which Dame Judi played "Hazel Wiles."
So when the BBC released these the cast list lists everyone who was ever in a production for that series of the BBC 2 Play of the Week and IMDB dutifully follows along like robots thus adding to the confusion of American Viewers who saw "She Fell Among Thieves" in its alternate role as the premiere of the long running MYSTERY! series on PBS (and, later, A & E).
So, maybe Amazon will let you Judi Dench fans exchange your copies of "She Fell Among Thieves" for "On Giant's Shoulders" should that ever become available through Amazon.com
(it isn't now).