When Barkley summons the Bumpus hounds, they run out the front door and fall into mud, because the porch is missing. They are seen crawling out of the mud, with mud all over their legs. In the next shot when they are chasing Barkley, there is not a trace of mud on them.
When Big Dickie is ripping the wood porch off the house, in one shot the stairs are attached to the deck, and then in the next shot they are already on the ground.
When Leopold Doppler (Glenn Shadix) is being pelted by the gravy boats, he shouts "Rosebud" from Citizen Kane (1941) and "Top of the World, Ma!" from White Heat (1949). However neither of these films were released at the time the movie was supposed to take place, the summer of 1940.
The movie is supposed to be set in 1940, but when the kids ride their bikes through the industrial part of town in one scene they pass a parked 1951 Packard 200 on the left side of the screen.
The film features an homage to The Good, The Bad, and The Ugly, when Ralph is on his way to the epic top battle. But the film is set in 1940. The film being referenced didn't come out until 1966, making this reference about 26 years too early.
Ralph's father mentions that the "Exposition" is going to open soon. The Century of Progress Exposition, a.k.a. The Chicago World's Fair, opened on May 27, 1933, when Jean Shepherd was 11 years old. The movie takes place in summer, not spring.
The movie mentions the Century of Progress Exposition of 1933 & 1934 as a current event, though the previous movie, "A Christmas Story," is set circa 1939 or 1940. In the gravy boat riot sequence, Leopold Doppler, Manager of the Orpheum Theater, announces that one of the movie-star theme china pieces, "your Sonny Tufts Big Boy platters," already is on the trucks being shipped to the theater. Tufts made his movie debut in 1943 in "So Proudly We Hail!"
When the gravy boats are being thrown at the theater, they make sounds as if shattering on the floor but are obviously bouncing and intact.
In the gravy boat riot sequence, Orpheum Theater Manager Leopold Doppler announces that part of the movie bill is a documentary on the exports of Kuala Lumpur. Kuala Lumpur is a city, not a country; it was the capital of the British colony of Malaya (now known as Malayasia). The major trading port in the region was Singapore.
When they are at the exposition, The San Diego LDS Temple (dedicated in 1993) is clearly visible in the background for a brief second.
Cleveland's Terminal Tower skyscraper is clearly visible in the scene outside of the store where the boys buy a hand-painted top. There are no buildings this tall in NW Indiana.