This is the third episode in the entire series that does not end with a punch line or any audience laughter; the other two being The Comic Book Store Regeneration (2015)(S8E15) and The Commitment Determination (2015) (S8E24).
Penny asks Leonard who her favorite Backstreet Boy is, and he tells her that she is team *NSync all the way. Nick Carter from BSB played Kaley Cuoco's boyfriend on 8 Simple Rules (2002) and The Hollow (2004).
Elon Musk also appeared as himself in episode 1.6, A Patch, a Modem, and a Zantac (2017), of Young Sheldon (2017).
Title Reference: The title refers to Sheldon and Amy reestablishing their platonic relationship.
Leonard states that Penny's birthday is December 2nd, but not the year she was born, nor her age.