Next lame electric question

[Kali]

See my thread from yesterday for background.

So I went and got a gfci receptacle and put it together and it all works fine. The original box is metal and I just stayed with that because I am cheap and lazy. The bare ground wire was attached securly to a green screw in the back of the box.

Reading the instruction sheet a little more closely, it seems to say to have a jump wire from that spot to the ground screw on the receptacle itself. Oops. Do I really need to do that? There seems to be plenty of contact where the receptacle is attached to the box.

Of course if that had been done to the original receptacle it would have stayed grounded when the screws fell out or were removed.