IO540,
As rustle says there is the initial test and then the renewal every 25months or less.
Examiners can not base a clear cut fail / pass with regard to minima on personal opinion. The reason being that the candidate who failed for using a DH of 300ft when it should have been 500ft (IR holders DH 200ft) could appeal to the CAA. Thankfully such an appeal is a waste of time because the CAA will simply say that the absolute minima which must be used is 500ft DH.
So with the CAA saying that the absolute minima is 500ft DH and 600ft MDH, the Examiners using that as a standard, the instructors teaching that as the way it is to be done do you honestly think that they are all wrong?
The IMC rating will not be round in the long term. Changes in airspace and European licensing will ause the end of the IMC rating or make is unuseable. What we are waiting to see is if a second class IR for those that can't get the IR will have requirements that are simpler to apply such as IR minima plus 300ft and RVR/VIS+1000m. That kind of limitation would be easy to understand, easy to apply and easy to understand.
Regards,
DFC