Even the CAAs response is confusing:
(this does not apply if revalidation was by proficiency check).
this is only correct if the proficiency check is completed early, i.e. greater than 3 months from the expiry date, then the new rating runs from the date of the proficiency check
however,
if the proficiency check is conducted within the last 3 months of the rating THEN IT DOES APPLY
All the JAA examiners signed a declaration of knowledge to say they understood all of this! But it was a long time ago!