Hi,
Welcome to the Forum.
I can't help much, but just to say that the Japanese hallmarks shown in your images do appear to be the correct ones for 850 platinum.
See:
http://www.925-1000.com/forum/viewtopic ... 38&t=28521
The Hattori mark also looks like the one attributed to that firm.
Hopefully someone else can add some more information.
Trev.