The Danish F68 telephone type is shown at an office desk in the start of the movie, set in 1967. This telephone was introduced in 1968.
In the film a street guitarist plays the song "Shadow of a Gypsy" by danish rock band Ache, apparently in July 1969. The song was released in august 1970.
Teacher Lilian's Renault 4 has no seat belts. They were only compulsory in Denmark in 1976. Yet, the inspector's Peugeot 404 has modern seat belts.