Everything you need to know can be found in
LASORS 2004 (warning 4.7Mb download!)
Section C1 covers JAR-FCL PPL (Aeroplane), and on page 107 of 610 you will find
An applicant shall be deemed to have successfully completed the theoretical examinations for the JAR-FCL PPL(A) when awarded a pass in all of the above examinations within a period of 18 months. A pass will be accepted for the grant of a JAR-FCL PPL(A) during the 24 months from the date of successfully completing all of the theoretical knowledge examinations.