When Dieter is at the border the GDR and they mention that Roy Black is at it's border, he starts singing "Tanze Samba mit mir", the german cover version of the Italian song "A far l'amore comincia tu (Liebelei)" by Raffaella Carrà. Not only did this song was released in 1976, 4 years after the movie's setting, the german version was never sang by Roy Black. It was sang the first time by Tony Holiday in 1977.
When the police officer states the day he said that it is Wednesday, the 26.08.1972. However the 26.08.1972 was an Saturday.
At the GDR checkpoint a portrait of Erich Honecker is hanging on the wall, as it is typical to have a portrait of the country's leader. However Erich Honecker wasn't the head of state in GDR until 1976. In 1972, when the movie is partly set, there should have been a portrait of Walter Ulbricht.
In the asylum a nurse is listening to "Fremde oder Freunde" by Howard Carpendale, a song that wasn't released in Germany until 1976, 4 years before the movie's setting.
When Dieter mentions the soft porno "Beim Jodeln juckt die Lederhose" it is recognized by others. This movie however was released in 1974, 2 years after the setting.
When Dieter, Petra and the boss are standing in front of Castle Neuschwanstein the microphone is visible on the top of the screen.