My understanding
This is what I understand of the IR Renewal/revalidation question.
Revalidation is a flight test completed within the expiry period, ie the IR is still current and valid. In the UK this allows you to alternate between conducting the test in the SIM one year and the aircraft the following year. The MEP however must always be conducted in the aircraft.
Renewal is if the IR is expired (with the 5 years), even if it is one day out you must renew and this requires that the flight test be conducted in the aircraft only. You cannot do a renewal in the sim.
As far as I know there is no difference in what is required for the flight test for a revalidation or renewal, however if you do allow your IR to expire past the 5 year mark then it is a full IR skills test with a CAA examiner.
That is my understanding but I'm sure someone here who is much more conversant with JAR FCL will be able to advise if any of that is incorrect.