Emilie Krall was in Vienna with her husband Franz Jauner in the 1870s, not in Germany, as suggested in the movie. Also at that time she was not performing anymore and was only singing for private parties. She wouldn't have signed a contract for a theater in Dresden.
The story that the performance of "Die Fledermaus" was a flop in the "Theater an der Wien" is a rumor, cause because another oper was scheduled at that time at the theater (Verdi's Ernani). In real life the operetta had 199 performances within 14 years (despite in other cities the operetta was a bigger success).
A poster announces the play "Angot - the daughter of the hall" on Tuesday, 13th April 1872. However that day was a Saturday.
Franz von Jauner was not working at the "Theater an der Wien" in 1872, as suggested in the movie, as he was a member of the "Carltheater" at the time.
The movie suggests that Franz von Jauner came to Vienna only in the 1870s after a request. In real life he was working in Vienna most of his life, e.g. as a member of the Burtheater and in 1871 he was working at the Carltheater, before he joined the Vieanna opera house.
In the restaurant scene in 1874 Johann Strauß is asking Franz von Suppé about the success of his "Donna Juanita". This operetta was released only in 1880.
Johann Strauß' operetta "The Queen's Lace Handkerchief" premiered in 1880 while Franz von Suppé's operetta "The beautiful Galathée" premiered in 1865. In the movie both operettas premiere at the same time.
In the movie Franz von Jauner joins the Carltheater after the performance of "Die Fledermaus". However Jauner joined this theater in 1871 and was working there until 1878, while "Die Fledermaus" premiered in 1874.
Franz von Suppé's operetta "Fatinitza" premiered in December 1876, after the premiere of Johann Strauß' operetta "Cagliostro in Vienna", which premiered in February 1875. In the movie it is the other way around.
The play "Madame Angot's daughter" did premiere on the 4th December 1872 in Brussels, not in April 1872 in Vienna. It was performing in Vienna only in 1877.