Love and Cheese / Weighing Harold - S4-E7
Continuity mistake: Weighing Harold: When Arnold shows Harold his reflection in the water, the reflection of his tooth is not reversed, it is on the same side of his mouth. The second time his reflection is shown, it is reversed. (00:16:37)
Love and Cheese / Weighing Harold - S4-E7
Continuity mistake: Lila was pretty much entirely underwater in a "standing" position when Arnold rescued her, how come suddenly the water only reached her knees?
Love and Cheese / Weighing Harold - S4-E7
Plot hole: Love and Cheese: Arnold and Lila go to the Cheese Fair together in this episode. However, the episode "Operation: Ruthless" also takes place at the Cheese Fair, and it is stated in that episode that the Cheese Fair is an annual event. It can't be that this episode takes place a year later, as the series takes place during the same fourth-grade school year.
Back to School / Egg Story - S4-E8
Other mistake: Back to School: After Principal Wartz tells Phil he will find a classroom for him, it cuts to a shot inside Mr. Simmons' classroom. If you look at Sid in this shot, the lower half of his body is cut off. Phoebe's right foot is also layered over him. (00:03:58)
Back to School / Egg Story - S4-E8
Other mistake: Back to School: After Phil completes his long division on the chalkboard and it cuts to a shot of Arnold, the shot is flipped, with Arnold's hair being the most notable giveaway. (00:04:43)
Back to School / Egg Story - S4-E8
Other mistake: Egg Story: When Arnold tells Helga, "I know you don't like me, and frankly, you're not my favorite person either," his mouth disappears twice. (00:14:51)
Back to School / Egg Story - S4-E8
Continuity mistake: Egg Story: When Arnold shows the little chick to the class, Phoebe is sitting behind Harold, but she is suddenly standing in the next shot. (00:22:30)
It Girl / Deconstructing Arnold - S4-E9
Continuity mistake: When Eugene breaks into the area with the dogs, you see the pedals of his bike tossed into the air, but the pedals fell off on the other side of the street.
Weird Cousin / Baby Oskar - S4-E11
Continuity mistake: Weird Cousin: When Lila tells Arnold, "Going to a movie together sounds kind of like a date," the way she holds her book changes between shots. (00:01:41)
Weird Cousin / Baby Oskar - S4-E11
Continuity mistake: Baby Oskar: In the beginning of the episode, Suzie is ironing Oskar's pants, and the laundry basket is on the floor beside her. Suzie picks up his pants and lays them out on the ironing board, and in the next shot, the laundry basket is suddenly in her hands, and the pants are in the basket. (00:12:21)
Weird Cousin / Baby Oskar - S4-E11
Continuity mistake: Baby Oskar: In the shot where Suzie tells Oskar, "As long as the baby is here, he's going to have to come first," the stove is drastically further away from the door than usual. (00:13:21)
Weird Cousin / Baby Oskar - S4-E11
Continuity mistake: Baby Oskar: When Suzie says to Oskar, "Tomorrow, tomorrow, tomorrow. That's all I ever hear from you," she sets the baby bottle on the table. In the following shots, the bottle is nowhere to be found on the table. (00:15:23 - 00:15:57)
Weird Cousin / Baby Oskar - S4-E11
Continuity mistake: Baby Oskar: When Oskar asks Suzie to make him breakfast, there are two baby food containers on the table. Later on, when Suzie is on the phone and Oskar walks back into the kitchen, the containers are gone. (00:16:14)
Weird Cousin / Baby Oskar - S4-E11
Other mistake: Stephen Viksten is credited twice for voicing Oskar.
Weird Cousin / Baby Oskar - S4-E11
Continuity mistake: In "Baby Oskar" when Suzie answers the phone there are 12 buttons on the phone, but when she is sitting on the bed there are 9 buttons.
Weird Cousin / Baby Oskar - S4-E11
Continuity mistake: In "Baby Oskar" the apartment number on the door to Oskar and Suzie's apartment appears and disappears multiple times throughout the episode.
Grandpa's Sister / Synchronized Swimming - S4-E12
Continuity mistake: Synchronized Swimming: In the pool scene at the beginning, we see a close-up shot of Connie and Maria. In the next shot, they are nowhere to be found. The three kids surrounding the pool in the beginning also disappear. (This happens because the opening shots are reused from the episode "Sixth Grade Girls.") (00:12:01)
Grandpa's Sister / Synchronized Swimming - S4-E12
Other mistake: Synchronized Swimming: When the boys take off their jackets during the swimming tournament, Arnold's jacket is floating in mid-air, and the left side of Eugene's jacket is also in mid-air. (00:20:45)
Grandpa's Sister / Synchronized Swimming - S4-E12
Continuity mistake: Synchronized Swimming: When the boys take off their jackets during the swimming tournament, Gerald's boots change from brown to black mid-shot, and when the camera pans over to Stinky, his boots are also black instead of brown. (00:20:45)
Grandpa's Sister / Synchronized Swimming - S4-E12
Continuity mistake: Synchronized Swimming: When the boys take off their jackets during the swimming tournament, Sid is missing from the group. When the boys dive into the pool, he returns. (00:20:46)
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.