The very first rough draft of "Scary Movie" (aka Scream) was written on April 5, 1995. There's only one known copy of that script and it's in the hands of a private collector. This is the earliest known draft to exist, known as the undated second draft. There are several differences you may notice like location (Bayboro, NC instead of Woodsboro, CA), extended and alternate scenes, and even a few surprise character names (although this is the draft where "Gayle Storm" was changed to "Gale Weathers.").
Scary Movie (aka Scream) - Undated Second Draft by Scream-Thrillogy.com on Scribd