I've been doing quite a lot of reading on this lately. It's something that the industry doesn't apparently want to face.
Fume events take many forms. The obvious one is the 'cabin full of smoke' scenario. That one can't be hidden. Sometimes there is the well known 'sweaty sock' or 'wet dog' smell which is usually just an annoyance but has caused sickness in many cases. Usually not many people are taken sick due to different tolerances. Airlines try to spin these things as 'smell events.' This reduces the importance in the eyes of the public. They talk of the 'nocebo effect' in another attempt to play it down. You don't actually need a smell there to be taken sick. It's a function of your 'toxic body burden.' Thats why crew tend to be affected more than passengers. They're loaded with organophosphates. Fortunately most have liver enzymes that can detoxify the system. A few don't.
I think that the Change list is an underestimate of the true extent of the problem. There are many more. Check the AAIB report into G-EUYB (also on the list). Some of those on the list can't be hidden. Take, for example, the case of G-EUUZ on 3rd October. This was a flight from Gatwick to Malaga which diverted to Barcelona. I've seen it described as a fume event and / or a medical emergency. It hit the headlines due to shoddy customer service. No other details available. It seems that we need a leak or whistleblower to make this sort of thing apparent. It's a shame really as there are some seriously nasty particles floating around the cabin when we fly.