In the scene at the print shop, Penelope speaks with an Irish accent when speaking with the printer. Nicola Coughlan is Irish in real life.
In the scenes where Anthony is interviewing ladies of the Ton and crossing out names in his book, two of the names are Lady Julia and May Quinn. The author of the Bridgerton series is Julia Quinn
When Kate, Mary and Edwina arrive at the ball with Lady Danbury, a string quartet version of Madonna's Material Girl can be heard.
In the 2nd book of the Bridgerton Book Series by Julia Quinn Kate, Edwina and Mary Sharma actually have the surname Sheffield. It was adjusted to depict a more diverse image in the TV series.
At the ball, Kate asks Lady Danbury about the Duke of Suffolk, and mentions "Debrett's." She is referring to Debrett's Peerage, a guide to the British aristocracy, founded in 1769. Still published, it lists all peers, their titles and their heirs presumptive.