Revealing mistake: When Lizzie awakens on the morning that Edith gets released, Edith doesn't respond and Lizzie goes to her bed to "mourn" the passing of her friend. Except that Edith is still breathing.
Revealing mistake: For a prison governor/warden, Mrs. Davidson (Erica) would presumably earn a modest upper middle class salary. Yet here she is on the phone, in the foyer of her home, wearing an elaborate house dress, surrounded by very stellar furnishings. But then she answers a knock at the door, and opens it to reveal a very ugly vertical striped wall mere feet behind her visitor. Obviously indicating that she either lives in a dim-tenant or low-scale apartment, or this scene was shot in-studio.