During the final scene, Penny is wearing the same top she was wearing when she met Leonard and Sheldon for the first time in the Pilot (2007).
Penny's maiden name was planned to be revealed when Sheldon calls out their names during his and Amy's acceptance speeches, but in fear of that moment upstaging the rest of the scene, it was decided at the last minute not to do so. Therefore, Penny's maiden name remains undisclosed. ** Never disclosed but hinted at from a parcel she received. Penny Teller. A nod to Pen and Teller, Teller who also appeared as Amy's father.
Chuck Lorre had Ed Robertson record an acoustic version of the show's theme song to recreate the demo version that Robertson first recorded for Lorre before the show started.
Penny's maiden name was never believed to have been disclosed during the series' run. However, it has since come to light that Penny's surname ("Teller") was revealed on a package in episode S2E18, The Work Song Nanocluster (2009), an obvious nod to Penn and Teller: Penny Teller. Some people have noted that in episode S2E15, The Maternal Capacitance (2009), Penny cries "My mom could have said "BOB, get over it. She's a girl, move on", giving her father's first name as 'Bob', but when they finally cast the role of Penny's father in S4E9 (The Boyfriend Complexity (2010) Penny's father tells Leonard to call him "Wyatt". Some have jumped to the conclusion that 'Wyatt' is her father's last name - Bob Wyatt - but that would mean he warmly told Leonard to coldly call him by his last name. This was clearly just a continuity error, the writers simply forgot they had already named him.
Amy's tiara is presumably the same tiara that Sheldon got her as an apology gift in The Shiny Trinket Maneuver (2012) and which she wore during her wedding in The Bow Tie Asymmetry (2018). In the final scene, Penny can be seen wearing the heart locket that Leonard had given to her in The Bon Voyage Reaction (2013), and Bernadette wears the star pendant she got from Howard in The Countdown Reflection (2012).