In season 3 episode 6 "Death Lives", Peter meets Quagmire for the first time on a navy vessel. In this episode, however, when Peter goes back in time to when he is 18, Quagmire and him are at the same country club ball. Furthermore, in season 7 episode 10 "Fox-y Lady", Quagmire's drivers license says he is 61 years old, meaning him, Peter, and Lois would never have been the same age at the country club ball at the same time.
In this episode, when Peter travels back to 1984, he's 18 again. Brian sees Lois and exclaims "18 year old Lois! Son of a b***h!" But in an earlier episode, "Let's Go To The Hop", Lois tells Peter she's 2 years younger than him.
Death said he was taking Peter to the exact moment in time that he took him to the first time they time traveled, but Death actually took Peter to a moment almost 2 minutes after the point in time they arrived the first time. For example, Peter and Cleveland "slapped 5" several times the first time Peter arrived, but Cleveland was nowhere to be seen the second and subsequent times Peter returns to the pool in 1984.
Brian says Never Gonna Give You Up was written by a gay guy. Rick Astley isn't gay. He's bisexual.
The entrance to Hogwarts is normally visible, no need to "look from just the right angle". Quagmire might be confusing it with the entrance to Platform 9 3/4, although that is not visible at all. Instead, you have to walk into what appears to be a wall to get through to the other side.
When kids fade back into existence in the picture, Chris appears first, even though Meg is the oldest.
The whole scene is a parody of Back to the Future, a time traveling classic. In the movie, Marty is in the middle of the picture. In this episode, the picture mirrors that of the film. It had nothing to do with who was oldest.
At the country club dance, when Brian starts playing 'Never Gonna Give You Up' by Rick Astley, the year is 1984, but it wasn't released until 1987. But Brian comes from modern times, so he has knowledge of the song. This is a direct reference to the scene in Back to the Future in which Marty McFly plays a heavy metal version of Chuck Berry's "Johnny B. Goode" in a 1950s school dance.
When Horace leans the ladder on the back of the bar and falls, it can be seen that a couple of the ladder's rungs are missing.
Peter gets sent back to the Summer of 1984. The Axel F. Theme from Beverly Hills Cop (1984), which Peter dances to and "sings along" with in the club wasn't released until the following winter.
When Brian is playing in the band at the dance and looks at the photograph, the guitar can still be heard though he isn't playing it at that moment.
When Peter and Brian are back in 1984, where Peter is 18 again, Brian says: "Wow, 18-year-old Lois." However in another episode, Lois says that she is two years younger than Peter.
In introducing "Never Gonna Give You Up", Brian tells the audience it's a song written by a gay guy. Rick Astley is actually happily married to his wife, Lene Bausager.
Brian makes an 80s band joke by telling Lois he'd like to "Wham" his "Oingo Boingo" in her "Velvet Underground." But the Velvet Underground was a 60s band.