Other mistake: When Spicoli supposedly takes a bong hit, you can see that he only inhales the air from the chamber - he takes his mouth away before the smoke gets to the top of the bong. (01:14:30)
Other mistake: Rattner and DiMone are game planning about Rattner's date with Stacy (Leigh). DiMone tells Rattner that all he needs to do to score with Stacy is play songs from side 1 of "Led Zeppelin IV" (Zoso). You then hear the song "Kashmere", which is on the album "Physical Graffiti".
Other mistake: In the scene when Mark Ratner asks for Stacy's phone number, there is a customer paying for a slice of pizza. Stacy tells the customer to pay $1.10. The customer gives her a dollar and change. She then gives him five cents back. The only way this could be right is if the customer gave her $1.15. If he could do that, why not the exact $1.10?