When Robin deletes Don's phone number officially, the camera shows a close-up shot of her phone. On her phone shows a list of her contacts after Don's number is removed. One of the contacts is named David Baker. David Baker is the property master for the show.
At the beginning of 'Unfinished', you hear Franz Schubert's Symphony No.8 which is popularly known as Unfinished Symphony which he composed in 1822 but left unfinished.
Marshall and Lily make several comments about what a good couple Ted and Barney would be. Neil Patrick Harris and Josh Radnor played a couple in the play "The Paris Letter".
Ted and Marshall discuss at length the fatal flaw of the Death Star in Star Wars, in that a single blast fired into a particular vent would reach the reactor core and cause the entire ship to explode and be destroyed. Specifically, they debate whether it was the fault of the "architect" who designed it, or the "contractor" who built it. It has now been explained (retconned in a sense) in Rogue One: A Star Wars Story (2016) that this was neither a design flaw nor a construction error, but was a deliberate act of sabotage by the "architect" (actually scientist/engineer) who designed it, Galen Erso, with the intent of providing a method for the rebels to destroy it.
In addition to the show's property manager, the close up of Robin's phone also shows her contact list to include Dan Blocker, TV's Hoss Cartwright from "Bonanza".