The player can use ammunition from AK-47s to rearm an M4A1. The two use different caliber munitions so this would be impossible.
During the mission "Overdose of Trouble", Maria asks Toni to drive to "the diner at Callahan Point" but in 1998 it's a doughnut shop. It's not until 2001 that it becomes a diner.
The song "Ruff Ryders (Remix)" is in the game; however the song was released in late 1998 and the game is set in early-to-mid 1998.
In the intro, a Ford Crown Victoria with a honeycomb grille (introduced in 2001) and 2001 New York-style license plate can be seen, when the game is set in 1998.
Liberty Jam's DJ refers to "Shook Ones (Part II)" as a new song, however, by 1998 the song was several years old.
Checker Taxi Model A-style vehicles are still being driven around in large numbers in 1998; by then they had mostly been retired.
A lot of the directional gantry road signs are blue; in the U.S. they tend to be green.
At Vicenzo's office, the lavatory is demarcated "WC", which is a UK term. In the US they are referred to as restrooms or bathrooms.
Harbor is spelled the UK way ("Harbour") on the gantry road signs.
In the mission "Snappy Dresser" Toni is supposed to make photos of Giovanni Casa in the woods wearing diapers. When he tells his mom about it, she replies: "Is this how you spend your time? Sneaking in the woods taking pictures of men?" Ma Cipriani couldn't know of Casa's and Toni's stay in the woods without seeing the photos.