All International Driving permits clearly state that they are invalid without the accompanying 'valid' national driving license. Having said that, 'he said she said' does not serve as a valid defence in court. You are accountable for your own actions and the duty of care rests with yourself. When you got into the car, it was with full knowledge that you, yourself, were unable to provide evidence of coverage, not only in written form, but even by statement. Therefore, you have no defence. I can only imagine how your excuses would sound had you hurt or killed someone. What would you have done then? Just left the country?
You are accountable for your own actions, whatever they may be.
Fr Bill