The title is a reference to "Angels in America," a two-part Pulitzer Prize-winning epic play by Tony Kushner. It was first produced on Broadway in 1993. Part One is known as "Millennium Approaches" and Part Two is known as "Perestroika."
Tom Durant (Eric Lutes) is still the station manager at KACL as of this episode, which makes him the second longest tenured character to hold that position, behind only Kenny Daley (Tom McGowan).
Niles (David Hyde Pierce) mentions a champagne from Connecticut served at a member of his wine club's wedding. To be called "champagne," it must be produced in the Champagne region of France. Otherwise it is called sparkling wine. Niles and Frasier (Kelsey Grammer) should know this distinction.
The use of the term, "Part III", in the title is not because the story is in three parts, but because it's Bebes third appearance as Frasier's agent. She will in fact appear in all eleven seasons, including the very last two episodes.