Other mistake: Ms. Perfect: When Lila and her father are eating dinner, as Lila's father says, "You sure are quiet tonight," the flap of Lila's can of beans is layered under her father's left arm. (00:19:04)
Hall Monitor / Harold's Bar Mitzvah - S2-E15
Other mistake: Hall Monitor: Helga tries to convince Phoebe that being hall monitor is the greatest job, with plenty of perks. Just as Helga says, "I couldn't let this job go to anyone; I picked you," Helga's hand is on Phoebe's shoulder, and part of Phoebe's shoulder is missing. (00:03:10)
Hall Monitor / Harold's Bar Mitzvah - S2-E15
Other mistake: Hall Monitor: At the start of the school assembly, when Principal Wartz thanks Helga for her month as hall monitor, Wartz's right arm is atop the lectern, with his fingers over the lectern's front edge. As Wartz gestures toward Helga with his right arm and hand, the fingers of his right hand oddly remain over the lectern's front edge. Then, after Helga announces she may volunteer again, the audience groans, and in the next shot facing Wartz, he has four hands at the lectern's edge. (00:01:35 - 00:02:00)
Other mistake: Ms. Perfect: After Lila answers Mr. Simmons' question about the inventor of the telegraph, as Phoebe says, "But I knew that," the book on Nadine's desk is overlapping the back of Phoebe's chair. (00:14:07)
Hall Monitor / Harold's Bar Mitzvah - S2-E15
Other mistake: Hall Monitor: When Helga chooses Phoebe to be the new hall monitor, as Phoebe starts walking to the stage, she is briefly layered behind the boy sitting behind her, and she is layered over Joey and the boy sitting next to him. (00:02:31)
Runaway Float / Partners - S2-E20
Other mistake: Runaway Float: After Nick talks about redesigning the parade float, Bob asks the kids who wants to ride on the float. Arnold then tells them it's great the way it is, and when the kids start saying, "Me! Me!", there is an animation glitch where part of Robert's head and hands get stuck in the air for about a second. (00:06:01)
Hall Monitor / Harold's Bar Mitzvah - S2-E15
Other mistake: Hall Monitor: During detention, the class helps Phoebe realise how much she has changed. When Helga wipes the window so Phoebe can see her reflection, in the first shot, Phoebe's reflection is not backwards as it should be. (00:10:45)
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.
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)
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)
Runaway Float / Partners - S2-E20
Other mistake: Runaway Float: When Bob asks the kids who wants to ride on the float, Arnold says to them it's great the way it is. In one shot, Iggy's hair is incorrectly coloured black instead of brown. (00:05:52)
Other mistake: Ms. Perfect: When Mr. Simmons tells the class, "I have a note from Lila's father," his right sleeve briefly turns green. (00:19:22)
Other mistake: Ms. Perfect: When the girls sabotage Lila's lunch, as Helga pours out Lila's milk from her thermos, the milk crosses an invisible line and disappears. (00:16:56)
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.