The two registration stickers on David's Jaguar E-Type's rear California license plate at first appear on the bottom corners of the plate (which is in itself a goof) but in later shots appear on the upper corners as is correct for California license plates.
After David runs into Jeremy with Amy's car, he was shown standing with his right arm outstretched parallel to the ground with a compound fracture of the upper arm, complete with the upper part of the bone protruding through his skin. A person with this kind of injury would not be able to hold their arm out that way since there would be no structural support from the upper arm; the arm would angle downward from near the point of fracture.
In one scene, Amy erases the "3" in the date on David's chalkboard and replaces it with a "4". In a later scene with Charlie, you can see that the "4" that Amy wrote earlier is now written in a different style.