The club in the opening, later identified as Club V, is the successor to Club Verdant, the club that originally stood above the bunker where Green Arrow and his teammates operated from.
Dinah's loft appears to be a redressed version of the apartment used by Oliver and Thea at various points in the series. It also includes a clock tower motif, referencing the clock tower headquarters of the Birds of Prey.
The first time Mia goes by "Mia Queen," rather than "Mia Smoak."
This is Stephen Amell's first and only Arrow episode where he does not make an appearance due to his deal that allowed him to appear in nine Season 8 episodes.
The real reason the backdoor pilot for the proposed Green Arrow and the Canaries series was created is because Marc Guggenheim was asked by The CW to make an additional episode to bridge the gap between the Crisis on Infinite Earths crossover episode and series finale, and also bring the episode order for Season 8 from nine to ten.