My larger Vapor 2 that I bought about 3 or 4 months ago says Japan. I don't know if they started making them in Japan and then moved the production to China, or if they were always made in China. Ken Onion posted on this site about visiting the plant in China where they are made, so I'd have to believe they are made there. Both sizes are probably made at the same site.
My wild guess would be that they were always made in China. Since the corporation (KAI) is in Japan, they may have been importing them from China to Japan and then exporting them from Japan to the USA with the Japan stamp itendifying where they most recently came from. Maybe that was a way to make the knife look a little better to American consumers. That wouldn't explain why they changed the stamp to China, but maybe it was in violation of import regulations and they had to change it.
Just my speculation. Anybody know for sure?