Ernst Thälmann gives a book as a present to Änne Jansen, who later reads to her husband from it. This book is a German translation of a Russian novel by Nikolai Alexejewitsch Ostrowski. The German title is "Wie der Stahl gehärtet wurde". The English title of this novel is "How the Steel was Tempered".
The movie mentions the actual 1932 Berlin Transport strike. However it is not mentioned that in this strike the Communists and National socialist were cooperating. The Nazis were joining it due to tactical reasons because of the coming Reichstag elections. The communists wanted to fight as a union against the social fascism and the labor union bureaucracy.
While not shown in the movie, very likely due to ideological reasons, from 1938-1940 Ernst Thälmann actually wrote letters to Moscow, addressed to Joseph Stalin, asking for help got get him free of his arrest. However Stalin refused to accept his request. Several reasons for that are known, like the Ribbendrop-Molotov-Pact of 1939 and also because due to his political vocabulary in the letters Stalin assumed that Thälmann is not a communist anymore. Also his rival Walter Ulbricht, another communist and head of state of the GDR during that time of this movie's production, was in Moscow and tried to convince Stalin not to accept Thälmann's request.
The final line in the movie is a quote from the novel "How The Steel Was Tempered" by Nikolai Ostrovsky, first released in 1932-34.