Gerd Heidemann's birthday is on the 4th December. However when he celebrates his 50th birthday on the yacht "Carin II" it is obviously spring/summer and it is not even remotely resembles winter time.
In the club scene with Thomas the song "Don't You (Forget about me)" by Simple Minds is played, which is released in 1985. The scene is set in 1981.
"Blue Night Shadow" by "Two of Us", which was release in 1985, is played in the club where Elisabeth arrives to meet Thomas. The scene however is set in 1981.