Here's a true story about why one set of appointments was missed.
Patient had an abnormal eye exam at the opticians. The conscientious optician wrote to the GP requesting a referral to the local eye department. Referral issued, and patient confirmed with GP.
After 6 months, with no appointment, patient checks with GP. GP confirms referral, and hospital confirm appointment issued, but not attended.
All very mysterious. GP re-requests. Hospital re-issues. Once again, patient enquires after a few months to be told appointment was not attended.
Curiouser and curiouser. Then, one day, out of the blue, the patient receives some forwarded post from the address they lived at 2 years before the opticians request. Patient manages to speak to hospital who admit having the wrong address (god knows where from - the GP had and forwarded the correct address).
Problem solved ?
Oh no, patient still missing some appointments - although patient now able to speak to booking desk after each appointment, so non-arrival of letters not a problem.
Patient does all they can to ensure everyone has the correct address. They all do, and swear there is no way post can be sent to previous address.
Post continues to be sent to previous address.
Finally, on a very busy day, the patient is asked to carry their notes between the orthoptics and ophthalmology departments. Patient opens said notes and discovers a sheet of pre-printed labels (with several missing) for the old address. Patient destroys sheet without telling anyone and order is restored. Patient recalls Fawlty Towers scene with diner and Spanish Omelette muttering "I've torn it up - you'll never see it again" to themselves.
You really couldn't make it up. And I haven't.