[Q] G4 Leather vs. G4 Plastic - Box Contents, Who else got an extra cover ?

Hi,
Just curious to know if there is any difference between the box contents of leather back cover and non-leather back cover ?
Because I recently bought G4 Brown leather and got an extra gold back cover in the box..
Does an extra cover comes with all color options ?
What about non-leather colors ?
Do they come with extra leather cover as well ?