When Mary hands her manuscript over to Shelley, she puts it on his desk with the back of the folder to the right side. Yet when he picks it up, the back of the folder is facing left.
After Claire goes into Lord Byron's bedroom, there is a shot of the candle chandelier. The cord used to raise and lower the chandelier, as it is holding up the chandelier, would be taut with the weight, yet there is a slack arc in the cord.
The end titles include the disclaimer that "The characters depicted in this motion picture are fictitious, and any similarity to the history of any person is entirely coincidental." Yet several of the characters, including Mary Shelley, Percy Bysshe Shelley, and Lord Byron, were obviously real people. The idea is that the words and actions of the characters are not claimed to be what the real Shelleys said and did, but it is still misleading. A better wording would have been "While based on true events and persons, all characters are fictional or are used fictitiously." The latter is more acceptable for films of this nature.
In the movie Mary Shelley is visiting a publisher directly and alone. In real life Percy Shelley was actively supporting her in search for a publisher.
The inspiration for "Frankenstein" came to Mary Shelley after a talk with Lord Byron and a personal explanation by his doctor John Polidori. In the movie she is seen watching an experiment with galvanic electricity way before that.
Several characters refer to the narrator of Mary's novel as "Doctor Frankenstein". In the novel Victor is a medical student, not a doctor. Popular culture began calling him Doctor Frankenstein in the 1940s, after Universal Studios' films gave the character a doctorate.
Lord Byron's play "Werner" was written from December 1821-January 1822, 3-4 years before the release of the novel "Frankenstein" in 1818. In the movie the play is ready in mid-1810s.
When Mary is in Scotland, a group of lumberjacks are cutting logs. While the blows are heard, the tools do not touch the wood.
When Mary is in Scotland and the lumberjacks are "chopping wood", the axe hits are heard instantly as the axes hit the wood, without the delay that would result from sound having to travel to where the main characters are walking.