When Lloyd first calls Diane, he gives 555-1342 as his phone number. But when Diane reads the message taken by her father, the number is 555-2342. Even though she has the wrong number written down, it still works.
When Diane's Dad gives her the ring as a graduation present, Diane slips it on her finger. Once the shot cuts away and comes back, she is still holding the ring with the ring bag in her hands.
In the break-up scene in the car the background changes completely. Before the line "You told your dad?" you can see an intersection and a hillside behind them, then after there is a yellow house and two parked cars.
When Diane is talking to Lloyd after his nose has been broken, the blood from his nose is inconsistent between shots.
Diane's father gets the news of her winning the Reed Scholarship by phone and rushes over to the nursing home to tell her. However Lloyd congratulates her on the phone for winning it the same day, saying he read about it in the paper.
When James Court is shown flirting with the woman at the mall in the checkout line, his credit card was shown being declined. The implication is that his troubles with the IRS (Internal Revenue Service) were responsible for this. However, until the IRS either freezes ones assets or seizes them, then credit card companies will not decline purchases unless the consumer was delinquent or overdrawn on their account.
As shown later in the film, when his attorney is discussing a plea deal with the IRS, they have taken no such action and, in fact, are attempting to obtain assets through forfeiture pursuant to his guilty plea.
After Lloyd and Diane break up, Diane gets in her car and starts the engine. Her automatic seat-belt, however, does not then slide back over her shoulder into place, which would happen as soon as the engine engaged. This is because she did not actually turn the car on, but the "car start" sound was simply added in post.
When Joe arrives at the party with his girlfriend, she says "I'll be in the kitchen, Joe", but her lips say "Bye, baby".
When Lloyd and Diane are walking through the crowd of people at the party, two people are seen arguing. One of them mentions going to summer school but his mouth is saying something different.
Lloyd sat with Diane at Bell Square, but when they show the mall they are actually showing Westlake, not Bell Square.
When Diane is racing to the nursing home after finding the money, all the cars she passes have California license plates.
When Lloyd is leaving his sister's apartment for the last time, mountains typical of Southern CA and not Seattle are visible through the front windows.