The JAA rules were written in collaberation with each of the 'CAA's' of the member states and agreed upon.
But you've missed the point, the JAA medical handbook '(the document agreed upon) calls for the test to be done in accordance with the manufacturers instructions, which say up to 2 mistakes can be recorded as normal.
The UK CAA has taken it upon itself to suggest that Mr Ishihara was wrong and that people should only be considered normal if they get no mistakes.