Throughout the series, Stephen and Matilda are both referred to as "Majesty". English kings and queens did not use the title "Majesty" until the middle of the 16th century, nearly 400 years after the setting of this series
When William Hamleigh rapes Aliena, he gets his henchman to cut off the right ear of her brother Richard to make her comply. But at the beginning of the following episode Richard's right ear is intact again with no sign of injury.
Rectangular quadripartite rib vaults, the type of the Gothic vaults used in the cathedral's nave, appeared in the second half of the 13th century (about a century later than shown in the series).