If there are some "statistics" out there that demonstrate objectively that the NRA rules are somehow superior at reducting unintentional shootings / ND's it's likely because of the last directive to unload the gun when you're not "using" it.
For people that use guns for protection, keeping it unloaded is impractical and in fact counterproductive. Cooper's rules are superior for people that live and work around guns that are always loaded; but you have to adhere to them.
Having said that, the NRA rules are well done and easy to remember, as long as you remember that a defensive firearm should "always" be ready to use. ;->
No; they only load the three or four that they intend to use. Such as the one in the sock drawer, glove box, pocket or day-timer. And yes, I have given you way too much information. If someone owns fifty guns, do they load all fifty ?