It is my position that the head of the 6mm screw is a Phillips/ISO. They do not have the JIS identifying dot on them. The smaller screws, 5mm, 4mm etc do have the dot and as such are JIS and a Phillips/ISO screwdriver will not fit them properly.
https://www.google.com/search?q=JIS+Screws&hl=en&rls=com.microsoft:en-us&rlz=1I7ADFA_enUS458&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=E5H0Tt6UB6rx0gG6zaX8Bw&ved=0CHwQsAQ&biw=1344&bih=678JIS screwdrivers will fit JIS AND ISO screw heads properly. hence it is easy for someone who has JIS screwdrivers to think they are the proper ones for the 6mm screw. They are. But so is the ISO.
The reverse is not true: ISO screwdrivers will not fit (properly) into JIS.
You can tell by inserting the tip into the screw in question if it has a proper fit or not, by careful observation.
http://www.instructables.com/id/When-a-Phillips-is-not-a-Phillips/step10/JIS-Japanese-Industrial-Standard/Particularly interesting are the comments which follow the article and add clarity to the issue. A mention is made that the 6x1.00 thread is not affected by the changes.
In the mid-60s an atttempt at unifying the different standards was made. All the threads were standardized to ISO, but some of the heads were not. A dot/dimple was added to the heads which remained as JIS. Since very few of the pre-65 non-dimpled JIS hardware survives, this is what we deal with now. 6mm - no dimple = Phillips/ISO.
I'm open for challenges on this position, but I've not experienced or read anything to the contrary. I use the standard Phillips #3 that comes with the American impact drivers and do not experience "cam out" on 6mm screws.
I've read a lot about the modern use of JIS hardware but it all relates to miniature applications like RC hobbies, electronics, etc., 5mm or less. They all have dimples.