Ann says that her birthday is in December. Later, she says she is an Aquarius. The astrological signs associated with December are Sagittarius and Capricorn. An Aquarius would have been born in late January or early February.
In the scene where Lee and Ann are at Lee's house and Lee reads Ann a passage from a book, Ann throws away the book irritated after a few sentences. In the next shot, the floor where the book should have ended up is empty.
When Deborah Harry is watching 'Mildred Pierce', we hear Ann Blyth's famous spiteful dialog on the stairway right before Joan Crawford slaps her. When we see the TV, we see a later scene, with Blyth in her nightclub dressing room.