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.
Part-Time Friends / Bio Square - S2-E19
Other mistake: Bio Square: While Phoebe and Stinky are telling the class about their science fair experiment, just as Phoebe shares that it was in honor of her hero, "I.P. Pavlov," watch as Stinky's eyes move off to the side of his head, then the animation layer of his eyes return to normal.
Arnold Saves Sid / Hookey - S2-E7
Other mistake: The clock in the police station looks like it says it's after 5:00, but school is in session.
Casa Paradiso / Gerald's Tonsils - S3-E3
Other mistake: Gerald's doctor's name is spelled "Murray Stieglitz" on the sign, but "Steiglitz" in the credits.
Benchwarmer / Cool Jerk - S1-E11
Other mistake: The names for the Green and Yellow teams' players are the same.
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.
Monkeyman! / Buses, Bikes and Subways - S5-E1
Other mistake: Buses, Bikes, and Subways: When Helga and Harold enter WrestleMania, as Harold says, "He lets me in all the time," the legs of the people sitting in the front row are cut off. Their chairs don't have any legs either. (00:22:03)
Arnold Betrays Iggy / Helga and the Nanny - S3-E10
Other mistake: Helga and the Nanny: Near the start, in the shot where Bob leaves the kitchen to answer the door, watch as Helga's mouth opens and closes with no animation whatsoever. (00:12:27)
Arnold Betrays Iggy / Helga and the Nanny - S3-E10
Other mistake: Helga and the Nanny: At the start, Miriam's dress is its usual purple colour, but when Inge arrives and walks into the kitchen, her dress is mistakenly coloured green. Her dress changes back to purple when she is shown again. (00:12:40)
Helga's Boyfriend / Crush on Teacher - S2-E14
Other mistake: Helga's Boyfriend: Near the start, Helga thinks of somebody to make Arnold jealous, then it cuts to a shot of Stinky in the cafeteria. In this shot, there are two men meant to be standing behind the counter in the background, but their bodies are actually embedded through the middle of it. (00:01:46)
Helga's Boyfriend / Crush on Teacher - S2-E14
Other mistake: Helga's Boyfriend: When Arnold and Stinky are on the swing set, Stinky tells Arnold that he is crazy in love with a girl. Arnold asks him who the girl is, and in the next shot of Stinky, his head disconnects from his body three times. (00:06:40)
Helga's Boyfriend / Crush on Teacher - S2-E14
Other mistake: Helga's Boyfriend: At the Stake Time roller rink, when Helga and Stinky are spinning around like a tornado, many of the kids are standing in mid-air. Brainy and Park are also standing in mid-air in an earlier shot where Helga tells Stinky, "Let's go!" (00:03:58)
Helga's Boyfriend / Crush on Teacher - S2-E14
Other mistake: Helga's Boyfriend: When Helga asks Stinky to be her boyfriend, as Stinky says, "Well, could you make it a Mr. Nutty candy bar?", you can see another Stinky sitting at the table at the far right. (00:02:16)
Helga's Boyfriend / Crush on Teacher - S2-E14
Other mistake: Helga's Boyfriend: At the start, Helga starts to profess her love for Arnold in the movie theatre. In this shot, Arnold's hair has four spikes on the right and three spikes on the left. Arnold's hair is supposed to have five spikes on the right and four spikes on the left. Also, just as Helga says, "your every action," Arnold's left side hair changes to four spikes mid-shot. (00:01:06)
Hall Monitor / Harold's Bar Mitzvah - S2-E15
Other mistake: Hall Monitor: After all the kids run into Phoebe, when Sid runs past her and her hat comes off, we can see that the hair above her scrunchie is yellow instead of black as it should be. (00:03:44)
Abner Come Home / The Sewer King - S1-E16
Other mistake: Abner Come Home: When Arnold wakes up and starts looking for Abner, as he walks into the kitchen, his hair clips through the doorway. (00:04:14)
Abner Come Home / The Sewer King - S1-E16
Other mistake: Abner Come Home: In Abner's flashback, Grandpa shows him how to get in and out of the door. We see grass outside the door, but what we should actually see are the stairs that lead to the door, not grass. (00:03:08)
Love and Cheese / Weighing Harold - S4-E7
Other mistake: Love and Cheese: When Arnold and Lila's boat is stuck at the edge of the waterfall, as Lila says, "Arnold, what will we do?" a piece of the boat next to Lila is incorrectly coloured like the background and the seat, so it looks like a hole in the boat. (00:10:14)
Hall Monitor / Harold's Bar Mitzvah - S2-E15
Other mistake: Hall Monitor: When Helga is deciding on the new hall monitor and it shows a shot facing the crowd, many kids sitting in the back are faceless. (00:02:20)
Hall Monitor / Harold's Bar Mitzvah - S2-E15
Other mistake: Hall Monitor: When Helga chooses Phoebe to be the new hall monitor, as Phoebe is walking to the stage, Iggy's hair is incorrectly coloured black instead of brown. (00:02:30)
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.