A CIA uses the console key and doesn't need a private header

 

Yes I have made many of my backups into cias like Mario kart

 

The CIA just uses your console key. There is no way to tell if your using a game you bought or not. Unless they check your nnid against what you have installed which it seems like right now they either won't or can't. Just don't use public headers for .3dz files you will get a temporary ban