My OH is another case. He has cancer and needs a monthly package of drugs for the rest of his life, including two chemotherapy drugs. The oncology dept foul up his appointments and prescription every sodding month. The blood test has to be a specific number of days before he starts the monthly drug regime - too early and they won't issue the prescription, too late and start date will be missed. How hard can it be? Well, apparently it's virtually impossible, because they can't even work out the start date - it's 28 days after the last start date - not difficult, but they simply can't get it right. Even when they get it right, they can't work backwards to work out the date needed for the blood test. Sometimes they book it a few days too early, sometimes a few days too late, sometimes they don't book it at all. Even after all that, on the start date, at the appointment made for collecting the drugs, at least half the time, the drugs havn't been ready.
So even for something as important as chemotherapy blood tests and drugs, they can't organise it properly. My OH has to make probably 5-10 phone calls every single month to either organise it all himself, or to change dates he's been sent that are clearly wrong. Once they even sent a blood test appointment for the day after he should have started the chemotherapy!
I know for a fact, he's "missed" several oncology appointments he didn't even know he had because he'd not received the letters, etc.
It's not until you become "heavily" involved with the NHS in respect of regular appointments and long term chronic diseases that you realise just how crap it all is. People who have limited dealings will no doubt think that a "lost" appointment letter is rare or that turning up for an appointment per letter on a date/time when there is no clinic is extreme - but in reality, it's pretty normal.