It is a great story. The movie was easily the most anticipated one of the golden era of Hollywood. When the theater manager saw Selznick show up with film cans he knew instantly what was about to be shown in his movie house. And when he announced to the audience they were about to see a special preview from Selznick Pictures they knew as well and broke into thunderous applause.
Absolutely. Selznick ordered the doors locked. No one could go in and no one could go out. How exciting it must have been to be in the audience that night.