After the opening sequence we see a three-engined Boeing 727 making its final approach to land at the Belgrade airport. In the very next shot, when the plane actually touches the ground, it's a two-engined DC-9.
Helicopter flying over hospital is a French Gazelle, that was not available to Yugoslavia in 1972 (first deliveries to Yugoslavia were in 1974).
In one scene, a chopper takes off from in front of the hospital, disappearing into the Belgrade skyline. In the distance, "Palata Beograd", the then-highest tower block on the Balkans, can clearly be seen. In 1972, when the story is supposed to be taking place, the tower was still being built and far from finished.
In the scene where they are exhuming the first smallpox victim, one of the policemen is holding a local version of the AK (M70AB2). That did not see service with police until late '70s.