Between 6 and 13.
The leather is hardened, and in most places, doubled up. The doubling definately kicks it into the 2 point range. If you don't like that argument, hardened leather is 'non-metalic plate,' putting it in the 2 point range.
It covers upper arms and chest. Chest is doubled, so that's the 6.
The possible extra 1 is for partial back, but I can't get a good look at it.
The possible extra 6 are for master crafted and in-genre. Assuming you can back up that piece with a reasonable costume with no obvious anachronisms, you should probably get those points. While covering the shoulders/upper chest isn't huge on the 'physical' armor points, they're one of your more visible locations, so good armor there is the key to your 'rp' armor points.
~Matt,
Marshal