Some of vehicles travelling on the street in 1976 were not produced until 1977 or later. The vehicles are as following Chevrolet Malibu (1978), Chevrolet Impala taxicab (1977), a parked Oldsmobile Delta 88 station wagon (1977). A double-parked Ford Econoline didn't have rectangular headlamps until 1979, following a minor facelift.
The paper with the "Iceman" headline that Mr. Freezy hands to Kuklinski has a story about Roy Demeo's body being found in the trunk of his car, though he is not yet dead in the movie and in fact Kuklinski and Mr. Freezy are discussing putting a hit on him in that scene.
When Richard meets Mr Freezy in the park, after he kills Leo, Mr Freezy gives him a newspaper with a headline that reads "THE ICEMAN MURDERS!!". There are two stories visible on the first page. One is about Roy Demeo's body having been found in the trunk of his car. If it wasn't for Mr Freezy commenting about Roy getting to them, we could've just assumed Richard had killed Roy off-screen. Also, the second story on the first page is titled "New mafia man" , but the text is about helicopters.