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)
Helga's Locket / Sid and Germs - S5-E7
Continuity mistake: Helga's Locket: After Helga leaves the boarding house through the basement window at the end, when it shows a close-up shot of the locket in her hands, Helga's sleeves are way longer than they should be. (00:11:37)
Helga's Locket / Sid and Germs - S5-E7
Continuity mistake: Helga's Locket: When Arnold is cutting a photo of Grandma in his room, there is nothing on his computer screen. Then, when Arnold starts to leave his room, a photo of Lila appears on the screen. (00:05:48)
Simmons' Documentary / Big Bob's Crisis - S5-E20
Character mistake: In the credits, Anndi McAfee's name is misspelled as "Anndi McAffee." (00:22:58)
Timberly Loves Arnold / Eugene, Eugene! - S5-E22
Continuity mistake: Timberly Loves Arnold: When Arnold, Lila, and Timberly are in the field together after the baseball game, Lila helps Arnold up and looks at her watch, which she wasn't wearing previously. Then, when Lila starts walking Timberly home, her watch has vanished from her wrist. (00:06:35)
Monkeyman! / Buses, Bikes and Subways - S5-E1
Continuity mistake: Buses, Bikes, and Subways: Helga wears a watch on her right arm throughout the episode. However, when Helga approaches Sheena's uncle Earl and wakes him up, her watch is missing, then reappears when Earl's boat sinks. It disappears again when Helga comes up from the water, then reappears a moment later. (00:18:59)
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)
Love and Cheese / Weighing Harold - S4-E7
Continuity mistake: Love and Cheese: When the sign for the Built-To-Hurl is first shown, it is spelled with a hyphen between "To" and "Hurl." When the sign is shown again, that hyphen is missing, then reappears a moment later. (00:07:19)
Timberly Loves Arnold / Eugene, Eugene! - S5-E22
Other mistake: Eugene, Eugene!: After Phoebe and Helga walk into the auditorium, the shot fades to inside the auditorium. If you look at Mr. Leichliter in this shot, you will see that his body is missing. As a result, his head and scarf are floating in mid-air. (00:11:50)
Arnold Visits Arnie / Chocolate Boy - S5-E12
Continuity mistake: Arnold Visits Arnie: When Arnold walks out of the movie theatre, he walks into Hilda and they fall over. In the next shot, they turn 90° counterclockwise. (00:06:45)
Dinner for Four / Phoebe Skips - S4-E5
Other mistake: Dinner for Four: When Arnold and Lila are talking to each other in the beginning, Lila says that she hopes to become a famous ballerina one day if she practices hard enough. In this shot, the stripe on her shirt is incorrectly layered over her gold button. (00:01:26)
Downtown as Fruits / Eugene's Bike - S1-E1
Continuity mistake: Downtown as Fruits: After Arnold and Gerald arrive at the school, it cuts to Helga crying about her play being ruined. When Phoebe taps her, her left arm is coming from the side of her cheese costume, but when the angle changes, it's coming from the front of her costume. (00:10:43)
Sid's Revenge / Roller Coaster - S3-E8
Other mistake: Sid's Revenge: When Sid is telling the police officer that he killed his school principal, Arnold's pants are the same colour as his skin, and his hat is not coloured in. (00:09:13)
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)
Curly Snaps / Pre-Teen Scream - S3-E6
Other mistake: Pre-Teen Scream: When the kids are sitting on Arnold's stoop in the beginning, there are two shots where Arnold's pants are the same colour as his skin, giving the sense that he has no pants on. (00:12:03)
Continuity mistake: Ms. Perfect: When Lila is wearing her new blue outfit at recess, she wears light blue bows in her braids, but when she is shown in close-up, she is wearing her regular green bows. There is also a small animation glitch with Lila's right bow. (00:15:22)
The High Life / Best Friends - S2-E10
Other mistake: Best Friends: When Gerald is first revealed during the fashion show, the curtains are transparent. They are never transparent in any other shot. (00:22:26)
Timberly Loves Arnold / Eugene, Eugene! - S5-E22
Continuity mistake: Timberly Loves Arnold: Throughout the scene where Arnold, Lila and Timberly are at the lemonade stand, Lila is wearing her gold button on her shirt. When Timberly asks Lila if she wants to come to the baseball game, as Lila says, "I'm sure that I'd love to," she moves her hands, and for a brief moment, you can see that she is not wearing her gold button. (00:05:46)
Love and Cheese / Weighing Harold - S4-E7
Continuity mistake: Love and Cheese: When Arnold and Lila's boat is stuck at the edge of the waterfall, Lila says, "Arnold, what will we do?", and when the shot changes, Arnold and Lila's hands both move to a different part of the boat. Lila's braids also go from being in front of her shoulders to behind them. (00:10:15)
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.