Kelsey teaches Carly about the X rating, where it came from, and why it no longer exists today.

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Sources:

Whatever Happened to the X Rating? by Entertain the Elk | youtube.com

X Rating | legal-dictionary.thefreedictionary.com

A History of the X and NC-17 Ratings | hollywoodreporter.com

A Brief History of the X Rating by Jason Bailey | vulture.com