At Nolan's funeral, Caitlin reaches out to Ava and takes her hand, similar to how Hanna reached out to Aria at Alison's funeral.
Dylan's line, "It felt like I was being buried alive one shovel full of dirt at a time," is a reference to how Alison was buried alive in the original series.
As the funeral is about to begin Dylan, Ava and Caitlin are walking towards the doors leading to the entrance, the song playing in the background is Mad World sung and performed by the cast of the TV Series Riverdale (2017).
Klea Scott (Dana Booker) played Jillian (Aria's boss) in the original Pretty Little Liars series.
Alison says it's impossible to guess the murderers in Agatha Christie's books. Any avid reader of Christie's works knows that the culprit is always the least likely person. In fact, Christie has mentioned it herself.