Answer: Thank you for your query.
You have obviously done plenty of research and correctly identified that exposure to wind driven rain as an important element where CWI has failed. It is important that the cavity remains unbreeched.
If it has been installed successfully for ten years with no indications of failure, then that is your best clue.
You might also look at other houses in the street and enquire if they have had CWI installed and have any issues.
For reassurance you can contact the CIGA to see if your installation came with a guarantee https://ciga.co.uk/contact-us/ and be sure your solicitor obtains any paperwork from the vendors.
You might also check if it was installed by a BBA approved installer http://www.bbacerts.co.uk/installer-approval/
Of course, the best advice is to have a proper building survey by an RICS qualified surveyor in your local area. Find one at https://www.ricsfirms.com/. A Building Survey is a bespoke report and you can ask your surveyor to pay particular attention to the CWI.
Otherwise, where properly installed and unbreeched CWI is a benefit to the energy efficiency of your home. I hope this is of assistance for you.