In Seth's flashback to his sixth grade class, young Seth tells young Luke that it's 11 months and 6 days until The Matrix premieres. The Matrix was released on March 31, 1999, so the date of that day in Seth's flashback is April 25, 1998.
Goof: Looking through old photographs of herself and Jimmy Cooper in high school, Kirsten told Summer that she got her perm because she had just seen Top Gun (which was released in 1986).
However, when Kirsten later met Sandy for the first time, he was campaigning for Mondale and Ferraro, which took place in 1984 - 2 years before Top Gun was released.
Goof: The scene where Taylor meets Frank in the hotel room, we see a lot of different dispositions of the pillows in the bed throughout the conversation, each time Frank shows up, the pillows are disposed differently.
Goof: The ringtone Bullit claimed is Persian, is actually, in fact, Indian.
Kirsten's birthday is February 2nd, 1967.
Julie's email address is: email@example.com
Bullit's email address is: firstname.lastname@example.org
When Ryan is walking into the bookstore, there is a sign on the window for Big Korea's biography finally coming out. In S3 The Party Favor, Summer's prom date is the lead singer for the band Big Korea.
Goof: When Seth goes up to Seattle there is a shot of the city skyline with the Space Needle in the foreground and the kingdome in the background. The kingdome was imploded in 2000, and there are now two new stadiums in its place. The kingdome later appears in another skyline shot.
Ryan and Taylor along with Seth Summer and Marissa graduated from high school at the end of season 3 which was in 2006. When you graduate high school you are 18, but the hospital bracelets said that Taylor was born in 1985 and Ryan in 1986 making Taylor 21 when she graduated high school and Ryan 20 when he graduated.
Dr. Roberts said he was thinking of working at Seattle Grace Hospital, however when Seth walks down the hall with him, there is a sign for Washington Mercy Hospital in the background.
The hospital Doctor Roberts works at in Seattle is 'Seattle Grace Hospital' the same fictional hospital that is in Grey's Anatomy.
Taylor's birthday is 07-09-85.
Ryan's birthday is 09-05-86.
(both as shown on the hospital tags)
However, in the season 3 episode The Journey it was stated that Ryan's birthday is March 19th, 1988.
In the toilette, there is a text on the wall saying "watch out for UFOs". It can be seen right before the woman in the alien costume steals their purse.
As Ryan is leaving Kirsten and Jimmy's house, a worker calls Kirsten the "Dragon Lady". This was a nickname Sandy used when referring to Julie Cooper at the start of season 1.
Luke Ward was not seen in the alternative universe, although it was hinted he never moved away from Newport because his brothers were seen teasing and bullying Seth which was what Luke use to do.
The nurse that gives Kirsten the letter that Marissa wrote to Ryan is the same nurse that Julie talked to in S3 "The Aftermath", when she was trying to get in to see Trey after visiting hours.
In the alternate universe there is a poster in the shopping complex saying that Johnny Harper is the Pacwest Surf Star. Johnny Harper was a friend of Marissa's in season 3 who was run over because of Ryan and therefore couldn't compete in the surf tour, although he was picked for it. Obviously because Ryan didn't exist in 'alt world' Johnny wasn't run over.
The Robert's address is:
4944 Pelican Grove,
Newport Beach, CA
The Cohen's address is:
6203 Bluffside Terrace,
Ryan is reading Twilight of the Superheroes by Deborah Eisenberg in bed.