I hope you agree with me, I use to work at the CAA issuing these licences. I also don't see what is so confusing
An applicant shall be deemed to have successfully completed the theoretical examinations for the JAR-FCL PPL(H) when awarded a pass in all of the above examinations within a period of 18 months counted from the end of the calendar month when the applicant first attempted an examination. A pass will be accepted for the grant of a JAR-FCL PPL(H) during the 24 months from the date of successfully completing the theoretical knowledge examinations.
The 24 months isn't for completing the checkride, its for APPLYING TO THE CAA FOR THE GRANT OF THE LICENCE as stated above. If you pass the checkride, and don't apply to CAA within this 24 months, exams expire!