The Little Pink Book/Field Trip - S1-E2
Continuity mistake: Arnold puts the pink book on top of a bookshelf at an angle. When Helga comes into his room moments later, the book is upright.
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)
Save The Tree / New Teacher - S2-E1
Continuity mistake: New Teacher: At the start, Principal Wartz writes Mr. Simmons' name on the chalkboard. Then, when Mr. Simmons walks over to the desk, the writing is missing from the chalkboard; it reappears a moment later. (00:12:07)
Continuity mistake: When Rhonda asks Lila if she wants to take the marriage predictor test, Lila is holding three books, but she is only holding one book in the next shot. (00:01:42)
Monkeyman! / Buses, Bikes and Subways - S5-E1
Continuity mistake: Buses, Bikes, and Subways: When Mr. Simmons shows the class the huge vat of chocolate, Phoebe points out that somebody is swimming in it. Then in the shot where Chocolate Boy rises up out of the chocolate, behind the vat, there is another vat which wasn't there before. (00:13:48)
Monkeyman! / Buses, Bikes and Subways - S5-E1
Audio problem: Buses, Bikes, and Subways: When Helga and Harold are running to catch the bus, as Helga says, "The bus is leaving, you dumb oaf," her mouth does not move. (00:14:49)
Monkeyman! / Buses, Bikes and Subways - S5-E1
Continuity mistake: Buses, Bikes, and Subways: After Helga and Harold first encounter Earl, it cuts back to the class on the bus. Phoebe is not sitting in the seat behind Arnold and Gerald, but in the next shot, she suddenly appears. (00:19:10)
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
Continuity mistake: Helga's Boyfriend: At the Stake Time roller rink, when Helga and Stinky are spinning around like a tornado, all the kids are standing around them, but they all disappear in the next shot. (00:03:58)
Helga's Boyfriend / Crush on Teacher - S2-E14
Continuity mistake: Helga's Boyfriend: At the Skate Time roller rink, when Helga and Stinky first start spinning around, there is a close-up of Ruth, and her skirt is its usual red colour. In the next shot, it changes to blue, the wrong colour. (00:03:55)
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
Continuity mistake: Helga's Boyfriend: At the library, when Helga tells Stinky to help her into her chair, there is a white folder and a yellow pencil on the table. Two shots later, they change to a red folder and a pink pencil. Two more shots later, the folder changes to green. (00:02:56)
Helga's Boyfriend / Crush on Teacher - S2-E14
Continuity 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?", the trays, fork, and Helga's hands are on the table. In the next shot, everything disappears from the table, then Helga's tray and fork reappear in the following shot. (00:02:16)
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)
Arnold Betrays Iggy / Helga and the Nanny - S3-E10
Continuity mistake: Helga and the Nanny: After Helga tells the kids that she took her father's belt instead of Inge, Arnold tells her that he can't believe she would do something that mean, then he gets up and leaves. He is not holding his lunchbox in this shot, but his lunchbox appears in his right hand a shot later. (00:20:12)
Arnold Betrays Iggy / Helga and the Nanny - S3-E10
Continuity mistake: Helga and the Nanny: In the shot after Helga tells the kids that her father fired Inge, Arnold's lunchbox has a baseball and baseball bat symbol on it, but two shots later, the symbol is gone. (00:19:52)
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.