Back to School / Egg Story - S4-E8
Other mistake: Egg Story: When Arnold tells Helga, "I know you don't like me, and frankly, you're not my favorite person either," his mouth disappears twice. (00:14:51)
Grandpa's Sister / Synchronized Swimming - S4-E12
Other mistake: Synchronized Swimming: When the boys take off their jackets during the swimming tournament, Arnold's jacket is floating in mid-air, and the left side of Eugene's jacket is also in mid-air. (00:20:45)
Grandpa's Sister / Synchronized Swimming - S4-E12
Other mistake: Synchronized Swimming: Right before the boys jump into the pool during the swimming tournament, Gerald's right eye seems to have lost its color. Right when Sid jumps into the pool, his eye is white again. (00:20:52)
Grandpa's Sister / Synchronized Swimming - S4-E12
Other mistake: Synchronized Swimming: During the swimming tournament, when the boys jump in the pool and it cuts to the crowd, Lila's dress and bows are incorrectly coloured blue, and they stay that colour for the rest of the episode. (00:21:04)
Monkeyman! / Buses, Bikes and Subways - S5-E1
Other mistake: Buses, Bikes and Subways: When Helga and Harold are running to catch the bus, as Harold says, "Ow, quit pulling my arm," Helga is frozen at the right side of the screen for a second before she starts moving. Also, her mouth doesn't move when she says, "The bus is leaving, you dumb oaf." (00:13:59 - 00:14:53)
Helga's Masquerade / Mr. Green Runs - S5-E2
Other mistake: Mr. Green Runs: When Green tells Arnold he can't be himself and needs to come up with some fancy words, Arnold is wearing a "Vote Green" button. Then, just as Green says, "I gotta get outta here," Arnold's button now reads "Voet Green" with Vote misspelled.
Sid the Vampire Slayer / Big Sis - S5-E3
Other mistake: Sid the Vampire Slayer: When Arnold and Sid are in the bathroom, there are two close-up shots of Sid as he speaks to Arnold. In them, the reflection of the door handle is not reversed in the mirror. Also, the style of the door handle in the reflection is different. (00:05:08)
Sid the Vampire Slayer / Big Sis - S5-E3
Other mistake: Sid the Vampire Slayer: While Sid stands in front of the mirror and points his rubber sword at Arnold and Stinky, the two ghoulish vampires, Arnold asks him, "How can we be vampires if we have reflections?" So when Sid is aware of his mistake, Arnold's eyes disappear and reappear in his reflection mid-shot.
New Bully on the Block / Phoebe Breaks a Leg - S5-E5
Other mistake: Phoebe Breaks a Leg: When Phoebe is about to be taken to the hospital, as Gerald says, "Now that is truly sad," there is an animation error where Arnold's mouth opens and closes for a split second. (00:14:42)
Helga's Locket / Sid and Germs - S5-E7
Other mistake: Helga's Locket: When Helga first sneaks into the boarding house, Grandpa is shown trying to open the locket. When the camera pans over to Helga and stops, a small part of Grandpa is still visible; then he disappears mid-shot. (00:03:25)
Helga's Locket / Sid and Germs - S5-E7
Other mistake: Helga's Locket: When Helga climbs to the top of the boarding house and looks at Arnold and Grandpa through the window, as Arnold tells Grandpa, "It's embarrassing and weird," Helga's left sleeve is incorrectly coloured pink instead of white. (00:09:02)
Helga's Locket / Sid and Germs - S5-E7
Other mistake: Helga's Locket: When Arnold and Grandpa are in the basement and Arnold says that they need the Shiska-Bob Stick, a small portion of the brown paper bag on the workbench is missing. (00:10:06)
Stuck in a Tree / Rhonda Goes Broke - S5-E10
Other mistake: Stuck in a Tree: In Arnold's imagination, when the gang passes the huge tree on the conveyor belt, notice how huge Sid is compared to Rhonda. It looks as if Sid was meant to be in front of Rhonda, but was instead improperly layered behind her. (00:07:43)
Stuck in a Tree / Rhonda Goes Broke - S5-E10
Other mistake: In the scene after the garbage dumpster scene, Buckley's lips disappear briefly while he's talking.
Arnold Visits Arnie / Chocolate Boy - S5-E12
Other mistake: Arnold Visits Arnie: When Arnold wakes up from his dream and he screams, his collar briefly loses its colour. (00:10:38)
Other mistake: When we first see Arnold walking Helga home after school, as Arnold says, "I never meant for this to happen," Arnold and Helga are briefly duplicated. As the shot continues, Arnold's backpack duplicates repeatedly. (00:11:22)
Gerald's Game / Fishing Trip - S5-E15
Other mistake: Gerald's Game: When Arnold is watching Gerald and the other boys play The King Rules through the window, as Gerald says, "There are a lot of terms," Arnold blinks, and his eyes are briefly not coloured in. (00:04:58)
Gerald's Game / Fishing Trip - S5-E15
Other mistake: Gerald's Game: When Arnold is watching Gerald and the other boys play The King Rules through the window, as Gerald says, "Are you implying that I'm not going to be king forever?", his eyebrows duplicate as he blinks. (00:05:16)
On The Lam / Family Man - S5-E17
Other mistake: A security guard in the train yard is drinking from a carton of milk depicting the boys. However, they had only been declared missing that afternoon. It is impossible to put out milk cartons that quickly.
Grandpa's Packard / Phoebe's Little Problem - S5-E19
Other mistake: Phoebe's Little Problem: When Arnold goes into Phoebe's room to cheer her up, the birdcage is reflected in the mirror on the wall, but the birdcage is too far to the right of the mirror, so it shouldn't be reflected. This error is shown again in a later shot where Phoebe tells Arnold, "And I'm very good at checkers." (00:09:13 - 00:09:45)
Answer: The show is based in present day times. Plus most cars aren't old fashtioned, I recall seeing a limo and not to mention a cherry picker, etc.