Character mistake: Lucas is seen placing flowers on Keith's tombstone, which states he died on January 23, 2006. In the next shot Lucas places a single flower on the grave of Jimmy Edwards, who died the same day and in the same scene as Keith, yet his tombstone states that he died on March 1, 2006.kakilroy
Plot hole: In season 4, Haley finds out she is pregnant. It is presumably around February, since it is right after Nathan and Haley's vow renewals and after the school shooting. If she, let's say, was already a few weeks along, she would not have given birth in June at graduation, but in October of the following year, since it takes 40 weeks or 9 months for a baby to go to full term, not 5 months.
Continuity mistake: When Lucas is with Keith at the graveyard in 4-10 and Brooke is standing in front of "Peyton's" tombstone, it says she died on March 1, 2006. Keith notes that she died on the day of the shooting. However in this episode Lucas visits Keith's grave where his tombstone says he died in January 2016.
Character mistake: Brooke and Rachel are in the clean teen meeting and they are asked if they want to join. After both saying yes, the clean teen president hands them their shirts but calls Rachel Brooke, and Brooke Rachel. You can see their hair colors and they didn't change spots when she went to get the shirts.
Continuity mistake: In this episode a sex tape shows a fling between Brooke and Nathan, and it is supposed to be from the past, but Nathan's hair is much longer and so obviously older in the video that it looks like it could have been filmed the night before, not from when he and Peyton were together.