The weathered and worn Pontiac Trans Am that Daniel Desario drives is a design that was available no earlier than 1979. Since the show takes place in 1980, it is highly unlikely that a high school student from a low-income family could afford what was then a fairly new car - and almost equally unlikely that it would look so aged within one year.
In the opening credits when Nick Andopolis has his school picture taken, he is wearing a black blazer over a T-shirt. When the black and white yearbook pictures are shown at the end of the opening credits, the blazer has disappeared and he is wearing only a long-sleeved shirt.
In "Chokin' & Tokin'", Lindsay grabs the "M" volume of the encyclopedia to look up "Marijuanna". She finds it in the back of the volume, even though it starts with "MA" which would be closer to the front of the volume.
At the end of the opening credits, a yearbook shows Nick, Lindsay, and Sam's pictures listed in a row. However, Nick's last name is Andopolis, and Lindsay and Sam's last name is Weir, meaning they would have been in opposite ends of the yearbook. Also, Lindsay and Sam would not be placed near each other, as they are in different grades (she is a junior and he is a freshman).