The members with diagnostics list is a list of people who have said they are happy to assist where possible. Because the you have to contact via PM it means the member has to be active on the forum to receive your message its not a given the member will have recieved your request.
There is also an annotation with a verification date in most listings. If this doesn't appear the member did not respond to a PM I sent in December, so chances of them responding to a request for help is pretty remote.

