The arrangement and number of gold jewels around Becky's eyes change between shots
Towards the end of the film, when Becky and Rawdon are eating dinner in their house, Rawdon throws the napkin that is tucked into his collar on the table. In the next shot, the napkin is back in his collar. When he stands to leave, the napkin is back on the table.
When Becky and Rawdon have their final argument, Becky has dark makeup around her eyes and on her lips. When she runs down the stairs after him, the makeup is gone.
While dancing, Becky wears dark black makeup on her eyes, streaked back almost to her temple. When the whole group reaches and looks up, the dark make-up is gone.
After the dance, Lady Gaunt is next to Mrs. Crawley. In shots from a different angle, she disappears.
The Duchess of Richmond's famous ball was held on the 15th of June, not the 17th as presented in the movie. (It is correct in the book.)
Early in the film when Becky is flirting with Joseph Sedley he offers her his bird because she likes things that come from India, but the bird is a Blue-and-yellow Macaw which is only from Central and South America.
Becky sings "Now Sleeps the Crimson Petal," a poem Lord Alfred Tennyson wrote in 1847 and appears in the Thackeray novel (1848) on which the film is based.
Because the novel concludes over a decade later (we assume on or before the present day for the author), and young Georgie, born in 1815 or 1816, is still only an adolescent, she would have sung it no later than 1840, which is well before it was published. However, the anachronism is Thackeray's and not the film makers'.
During the dance scene, a musician plays a metal flute, which was invented by Theobald Boehm around 1832.
When Becky Sharp comes to London, a modern-day street lamp is reflected in the coach's window.
The Song which Becky Sharp was dancing to is actually an Arabic folk song (AssalamAlekom) released in 2001.
"Now sleeps the crimson petal", published 1847, does not feature in the novel as stated below; Becky sings "religious songs of Mozart" to please Lady Steyne. Rawdon junior was born in 1816 and is still a child, so Lord Steyne's party takes place in the 1820s.
The song to which Becky dances in front of the King is an Egyptian song (Hakim - Salamo Aleikoum) that came out in 2010, so much later than the time where the story is supposed to take place.
When Becky watches her son leave in a carriage, the boom mic operator is briefly reflected in the carriage's rear window.
During the outdoor gathering at Vauxhall, George Osborne and Joseph Sedley ride in the row boat. A cable slices through the water, pulling the boat from the front.
When Joseph Sedley gives Becky a parrot, he says it's because she loves things from India. The Blue and Gold Macaw is native to South America.