I completely agree that anything created by an artist with the intention of being "Art" becomes "Art" the moment it is created. However I do not believe that that is the end of the story. Art is changed by both the context it was created in, its history and even the context it is viewed in and you cannot fully understand and appreciate the art without understanding that context. And as our knowledge and understanding of that context changes (for example by finding out that we have been lied to about the origins or history or piece of art or its artist) then the art changes with it (without ever stopping being art).