Other mistake: When Corie's mother arrives for dinner, she sits down on the trash can, and asks Paul to get her pink pills from her handbag. When Paul holds out the open pill box to her, the mom accidentally knocks it shut, but pretends to grab a pill anyway, and take it.
Other mistake: The first time Corie arrives at the apartment we see her climb each flight. For the last one, the one that's supposed to take her to the top floor, we can see the underside of another flight above her head. By the time she hits the top of that flight and her walk to her apartment door we can see there are no more stairs. The fact that they live on the top floor is discussed throughout the film, especially when addressing how exactly Victor Velasco can be their "upstairs" neighbor. (00:10:20)Maiasatara