Another (likely) indicator (but obviously extremely easy to fake) is that S&W magazines since the 1980’s all have plastic followers, often in bright or light colors and they tend to show at least trace evidence of having been loaded and used for live fire by dirt or trace filth on the follower. NIB 3rd Gens have magazines that appear as if no round of ammo has ever been loaded in to one.

Come to think of it, NIB 3rd Gens also had small round white or colored stickers right on the pistol itself with a number of a packer or inspector, these fell off easily but the presence of one also kind of sets the scene.