There's been some contention here on the forum on whether or not true JIS screwdrivers are produced anymore. Most makers seem to manufacture to some DIN spec. I think there's more on the Vessel website and if you search "JIS" on the "Tools of Japan" thread, you'll see some discussion. Apex bits, which are well regarded here, has some bits on their website that they refer to as "Japanese Philips"
http://apexbits.com/492J-CI-Apex-1-4-Japanese-Phillips-2-Hex-Power-Bits.aspx. You might try calling them, they could probably shed some light.
As an aside, I just purchased a #2 crosspoint Vessel and a #2 Philips PB Swiss. I tried each one on several fasteners on my 2001 Civic. The head of each fastener was marked with a very small cross symbol, and there was very little difference in the way the two drivers fit. In fact, the PB Swiss may have had the edge over the Vessel.