Continuity mistake: Most of Season 1 takes place in January of 2006, while Season 2 takes place in March of 1979. Molly mentions near the beginning of Season 1 that she's 31, and her father confirms this in episode 10 by mentioning that she was 4 years old during the events of the Sioux Falls massacre (season 2). In season 2, Molly's mother mentioned in episodes 1 and 4 that she's 6. It's also revealed in a flashback scene in episode 10 that she graduated high school in 1991 (most people are 17 or 18 when graduating high school). If you do the math, you'll see that there's an inconsistency in her age between Seasons 1 and 2. Apparently, 2 years were added to her age in Season 2.
Mommy's Little Monster - S2-E7
Continuity mistake: Miss Kringle's head is canted up and to the right as she lays on the gurney in the morgue refrigerator, but when Edward Nygma pulls her out, her head is facing straight up. Subsequent shots of her in the refrigerator her head is canted up and to the right.
Continuity mistake: During the street scenes it appears to be fall with leaves on the ground, grass green and streets and sidewalks dry. However, when police raid the park worker's house there is snow on the house roof and on the ground. When the police stake out the same house, there is no snow on the house roof or ground. (00:36:00 - 00:41:00)
Episode #1.6 - S1-E6
Continuity mistake: The district commander wears the rank insignia of a chief superintendent up until the final episode, when he suddenly appears with the insignia of the lower rank of superintendent.
The Secret Fate of All Life - S1-E5
Continuity mistake: The first time we see Detective Cohle being interviewed by the other two detectives, two of the beer cans on the table in front of him completely vanish between shots when he asks to see the rest of the discovery file.
Continuity mistake: In S:1 Ep.10 Maddie says she'll be 15 in a week. Season 2 picks up 6 months later. In S2ep5 Bosch uses Maddie's birthday to access a computer. Password is 01/10/01. This makes the date sometime in July of 2016. Then in S2ep6 George Irving is killed, and the end of watch broadcast lists his date of death as 7/24/2015. This error is reinforced in S2ep10 when they show a plaque being mounted to honor George.
Episode #3.5 - S3-E6
Continuity mistake: Sidney is attending a pre-wedding dance in the camp he is visiting wearing a light colored shirt. When he leaves the dance floor to chat with other attendees, he is now wearing a green sweater over his shirt.
Continuity mistake: Lund tells Gregorio that he got a text from a friend in DC, who ran the names of Yates and Blakely through a government database and found something. When it cuts to a young man walking, in the interior shot from inside the police cruiser the rearview mirror is missing from the windshield, but in the exterior shots the rearview mirror is properly attached. (00:26:10)