When Barkilphedro first reads the blackmail note from Doctor Hardquanonne, we are shown a shot of the full text of the note. Toward the bottom, it says, "You are rich...". Seconds later, we see close-ups of the note. Words have been rearranged on the page to make the close-ups more readable and the lower portion now says, "You will be penniless," - a phrase that didn't appear anywhere in the original text.
After swimming in the river, Homo, the wolf, is dry when he immediately attacks Barkilphedro. He is dry when pulled back into the boat after his second crossing of the river.
When Dea reaches through the curtain searching for Gwynplaine, she puts her left hand through the gap but it is her right hand that comes out the other side.
When Josiana wakes up and embraces Gwynplaine, she puts both her arms around his neck. In the next shot, only her right arm is around his neck and she uses her left to prop herself up.
Although a silent film allows convenient ambiguity, the story presents Gwynplaine's speech as clear enough to be understood by all other characters without impediment. Since Gwynplaine cannot close his lips, he could never form the consonants b, f, m, p and v. At least one of these sounds occurs in the vast majority of words in Gwynplaine's native tongue, English. Realistically Gwynplaine would be virtually mute, as actor Conrad Veidt was whenever wearing the Gwynplaine prosthesis.
The fictional comprachicos are banished from England by King James II in January 1690. This is even more fictional because James had not been on the throne for nearly two years on the date cited for this banishment.
The opening scene happens in James II's reign (1685-1688), but Lord Clancharlie is sentenced to death in an Iron Maiden. This instrument of torture was invented in 1793 for display in museums.
The clowns wear modern "clown" make-up in Queen Anne's reign (1702-1714). This appearance was not developed until the mid 1800s. Jo Grimaldi was the first clown to wear this style.
By the look of Gwynplaine and Dea, about 20 years pass between the prologue and the main part of the movie. There is no way Homo the wolf could still be alive after that amount of time.