In Scream 3 when Cotton's girlfriend is getting attacked, she runs into the study and locks herself in it. Then the killer stabs the door 3 times. When Cotton gets to the door, there are 5 holes. Where did those extra 2 holes come from?
Maybe it just didn't show him stabbing it the last two times? It did go from her scene to Cotton, and then him running in...so that is very possible it just didn't show it!