When Rick and friends find the rats and open fire on them, Boo gets blood splatter on his clothes and face. In the first couple of shots, there's a large spot on his cheek; in the next, the large spot is gone and the blood is more spread out.
Suppressors (silencers) are shown such as when test firing in the shop, to be almost completely effective even on rifles. In reality, rifle bullets are supersonic so are still very loud once they leave the gun; firing one, especially indoors, would require hearing protection or at least everyone would be cringing and/or covering their ears from the noise.
The guns shown being sold by Rick's father were AK47's which were very rare in 1984 and usually only the Egyptian models. They were being sold around $900 at that time. AK's didn't become more widely seen until the late 1980's when 2 Chinese companies flooded the US market with them at prices around $300. Gangs back then were using Uzi's, Mac-10's, Mini-14 or surplus weapons like the M1 carbine.
Richard Sr tells Ritchie to go inside, he got a cool ''Glock'' --This was in '1985' - Glocks were not Available in US market until after 1986 and then quite rare.
Rick offers his friend a "soda", but in Detroit, carbonated beverages are called "pop".
The bulk of this story is set in the early/mid '80s. However, Wershe Sr. tells his son that he is seeing someone about a "40 Cal". The .40 S&W cartridge debuted on January 17, 1990.
The film is set in 1985. In the Las Vegas scenes, the Fremont Street Experience canopy can be seen in some shots. Construction on the canopy did not begin until 1994, and was completed in 1995.