Other mistake: The FBI agents call for a taxi and official transportation from the Evans apartment and gave the address of 963 North Gilbert. However, the Evans lived at 921 North Gilbert. Since the FBI was at their apartment, you would think that they would know the address or exactly where they are in a Chicago project. (00:13:03 - 00:28:29)
J.J.'s Fiancee: Part 2 - S3-E18
Continuity mistake: At the beginning of the show, JJ's girlfriend is wearing a shawl and the buttons are miss-buttoned by one button. In the next scene, the shawl is buttoned correctly.
Answer: Carl did die of lung cancer, that's why she returned to her family.