The highlight of such occasions was the cotillion, a gamesy ritual for selecting partners that took its name from a frisky old French folk dance called the cotillon, or petticoat.

Look at this heckin boofer I found. (quoting twitter)

Cap-and-knee slaves, vapours, and minute-jacks!

No, it's not necessarily a plot hole. The show's history doesn't have to exactly match the show's 20th century background. (For example, Strife is still around in the 20th c. Hercverse, even though he died in the show.)