As Beau and Sarah are standing out front of the conference center after their initial meeting a cable car passes through the frame with an advertisement for a 2005 model Samsung flip phone on it, despite the established time frame of January 1997.
When Sarah is nearing her cab at the airport, there is a mix of yellow Ford Crown Victorias present, some of which feature the updated 1998 model design, which would not have been seen in January 1997.
When the characters are looking in the High School Yearbook for a picture of Beau, his name is listed first in the column of names, indicating that his picture would be first in the row of pictures. However, his picture appears last in the row of pictures.
When Beau and Sarah have just finished their night, and they decide to get a cup of coffee, Sarah grabs the cup handle with her left hand, but when the camera goes up close, the cup handle is in her right.
When Sarah meets Beau's 'son' Blake, Blake says he has just returned from Asia to his father. As Beau moves towards Sarah after this line, Blake can be seen behind Beau scratching his face. The shot moves to Sarah then back to Beau and the exact same shot of Blake scratching his face is used.
When Sarah and her father are in the kitchen, he sets a mug of tea in front of her. She reaches for the handle around the front of the mug, but then in the next shot, she's turning the mug from behind it.
At the end of Sarah and Jeff's discussion in his apartment towards the end of the movie, Jeff walks towards the door, leans back against the wall and crosses his arms. In the next shot Sarah walks past him and he has his hands in his pockets. As she walks out and closes the door Jeff takes his hands out of his pockets and crosses them again.
When Sarah looks at her mother's picture in her bedroom, the pink 8-Ball "Date Ball" is to the picture's left, next to the stack of books. In the next shot, it's clearly moved to the shelf above the books. Returning to the close-up of the picture, it's next to the books again. Next shot, it's again up on the shelf.
When Sarah is talking to Annie when she first gets to the house for the wedding, her hand moves between being on her shoulder when the camera is on her back to her hands being crossed when the camera is facing her.
In January 1997, Jeff jokingly tells Sarah that his family is like the movie "Titanic", and goes on to talk about nude sketches of himself - a specific reference to Titanic as opposed to any other Titanic movie. The movie wasn't released until December 1997. However, the nude sketches scene was used in advertisements some time before the movie release, so it is barely plausible for Jeff to make this allusion.
When Sarah and Beau are in his plane going down the runway, as a pilot, Beau would be wearing a headset to communicate with the tower or with air traffic control, but he isn't. However if we assume he has a private airstrip there would be no tower and he may have chosen to put on his headset later.