When Mrs. Wheeler bursts through the door, angry with Nancy about lying to the police she throws her purse down. When they get to the kitchen she throws the same purse down again.
The show is supposed to take place in November 1983, but a sign at the school (seen when Nancy is on the phone trying to reach Barb) mentions "Battle of the Bands on Friday November 28". In 1983, Nov 28 was on a Monday. The closest year it was on a Friday would be 1980 or 1986.
When Nancy is on the public phone speaking with Barb's mother, a poster for "Battle of the Bands" is to take place on Friday, Nov. 28th. Only the years 1980 and 1986 would have that date during that decade. The series is supposed to be from the year 1983.
The day after the pool party, when Nancy walks up to her locker she doesn't dial the combination. She just lifts the handle and opens the door.
When Steve steals Jonathan's pictures, a cell tower can be seen in the background.
When Eleven is looking at the bulletin board of photos from Nacy's childhood, there is a photo taken of a broken concrete sidewalk. This structure was created for the Tennessee Aquarium in Chattanooga, TN. Although the show is set in 1983, the aquarium was not built until 1992.
The Jack in the Box PEZ dispenser Dustin dumps out of his backpack was not released until 1999.
The police chief is seen wearing a modern day rubber band loom bracelet.
The Millennium Falcon toy that Dustin picks up and drops, hoping Eleven will make it fly, is not era-appropriate. The Millennium Falcon toys of the era had a sticker in the back in place on the hyperdrive exhaust vents. It wasn't til after 2000 that the Millennium Falcon toys actually had light-up exhaust vents with blue lights. In the show, you can clearly see that it's the model with the transparent plastic for the lights to flash.