Helga Blabs It All / Harold the Butcher - S3-E1
Continuity mistake: Harold the Butcher: Mr. Green's meat store has a shopkeeper bell over its front door that vanishes in some shots, then it reappears. For instance, the bell is gone when Arnold is in the store while Harold sits across the street, but we hear it jingle and then the bell reappears when Harold enters the store.
Helga Blabs It All / Harold the Butcher - S3-E1
Continuity mistake: Harold the Butcher: At Mr. Green's meat store, there are at least two instances that the word "MEATS" is misspelled as "MAETS" on the store's aprons. When Mr. Green gives Arnold the package for Grandma, Green's apron changes to the misspelling. Then, when Harold returns to help Green with the crowd of customers, Harold's apron has the misspelling.
Helga Blabs It All / Harold the Butcher - S3-E1
Continuity mistake: Helga Blabs It All: While Helga is in the ventilation shaft, when she calls Phoebe for help, the rope is tied around Helga's waist with a knot at the front, but it cuts to a closer shot and the knot vanishes.
Helga Blabs It All / Harold the Butcher - S3-E1
Continuity mistake: Helga Blabs It All: After Helga successfully snatches the message tape, when she rushes out of Sunset Arms the front door is missing its handles, but one handle reappears when Campfire Lass and other girls chase after Helga.
Helga Blabs It All / Harold the Butcher - S3-E1
Continuity mistake: Helga Blabs It All: Phoebe stops the Jolly Olly ice cream truck and gets inside. As they head toward Arnold's house, in the interior shot a rearview mirror appears on the windshield where there wasn't one. Then, when the ice cream truck is parked in front of Sunset Arms, there are some changes to its appearance.
Helga Blabs It All / Harold the Butcher - S3-E1
Continuity mistake: Helga Blabs It All: While Helga goes after the tape at Sunset Arms, room numbers repeatedly change/vanish, or doors disappear and reappear. Some examples: Door 3 vanishes when Helga lowers herself via rope the first time. When Arnold unfolds the attic stairway, the closest doors are 7 and 8, but when Arnold and Gerald run down those stairs, door 8 changes to door 1. When Grandpa talks to Mr. Hyunh, door 1 is now door 3. When Grandpa and Ernie enter Hyunh's room, door 7 becomes door 5. When Grandma exits door 4, it then changes to door 2.
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.
Arnold's Room / Helga vs. Big Patty - S3-E4
Other mistake: Helga vs. Big Patty: When Helga dreams about boxing Patty, as she steps back from her, she is standing in mid-air for about a second. (00:17:00)
Arnold's Room / Helga vs. Big Patty - S3-E4
Continuity mistake: In the locker room, Sid's hair goes from stringy to full and back to stringy.
Curly Snaps / Pre-Teen Scream - S3-E6
Audio problem: Curly Snaps: At the start, Curly talks to Arnold about how good it is to be ball monitor. When Arnold says, "Well, I never thought of it that way," his mouth stops moving after the word "it." (00:01:25)
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)
Curly Snaps / Pre-Teen Scream - S3-E6
Audio problem: Pre-Teen Scream: When Phoebe turns on her CD player and reveals her Ronnie Matthews posters in her room, she says, "Now to compose the winning contest entry," but her mouth isn't moving at all. (00:13:00)
Curly Snaps / Pre-Teen Scream - S3-E6
Continuity mistake: Pre-Teen Scream: When Phoebe shows up at Helga's house to pick her up for the concert, Phoebe is wearing a red outfit with a red scrunchie in her hair. Thereafter, for the rest of the episode, her red scrunchie changes to her normal yellow one in some shots. (00:15:46)
Grandpa's Birthday / Road Trip - S3-E7
Audio problem: Road Trip: When Miriam points out the Wheeler Inn and Big Guy Restaurant while driving, as Helga says, "I really don't think," her mouth does not move. (00:14:56)
Grandpa's Birthday / Road Trip - S3-E7
Factual error: Road Trip: Whenever Miriam and Helga's car is on a broken white line road, the two lanes are moving in opposite directions; lanes on broken white line roads are supposed to move in the same direction. (00:17:15)
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)
The Aptitude Test / Oskar Gets a Job - S3-E9
Audio problem: The Aptitude Test: When Mr. Simmons gives Stinky his folder at the start, Mr. Simmons says, "Boys and girls," but his mouth does not move. (00:01:08)
The Aptitude Test / Oskar Gets a Job - S3-E9
Continuity mistake: The Aptitude Test: When Arnold tells Harold that he missed practice, Harold shows Arnold and Gerald his blueprint, but he never turns the front of it towards them. However, in the next shot, the front of the blueprint is suddenly facing Arnold and Gerald. (00:07:32)
The Aptitude Test / Oskar Gets a Job - S3-E9
Continuity mistake: The Aptitude Test: After Mr. Simmons' conversation with Helga outside the school, he walks into the classroom, and the folders on his desk are in a messy pile. However, in the next shot, they are in a neat pile. The folders rearrange themselves in the following shots, and finally, when he looks inside Harold's folder, the rest of the folders disappear from the desk. (00:09:55)
The Aptitude Test / Oskar Gets a Job - S3-E9
Other mistake: Oskar Gets a Job: In the beginning of the episode, Arnold and Gerald overhear Oskar arguing with a man in his room. In the close-up of Arnold and Gerald as Oskar says, "You're a big man, aren't you?", Arnold's right eyelid is not colored in. (00:12:17)
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.