When Rudolf is having sex with Maria (Mary), a large tattoo on Max's upper left arm is visible through the poor makeup job.
Early on in the second episode, a prostitute offers Rudolf and his friends two bottles of Dom Perignon champagne, with the familiar bottle and label --"Gentlemen, special delivery just in from France" . Although it purports to be around 1886 (Wilhelm mentions "It's 1866 all over again", to which Johanne responds "It's been twenty years Wilhelm, don't you have anything else to brag about?"), Dom Perignon's first vintage was in 1921.
When Franz Joseph celebrates his 40th anniversary, he introduces Wilhelm as Prince Wilhelm. However, Wilhelm has been the Emperor of Germany six months prior.