Well to be fair it's a mess for them too. The problem is they don't know the cause, many NDD's have no biomarkers or imaging to test for, and even when they have it narrowed down everyone is different.
Getting diagnosed is an issue in and of itself. There are about 100 or so symptoms, both physical and cognitive. Most of those symptoms are often symptoms of other conditions like Thyroid problems, depression, etc. So you have to go through all of these other tests to rule out anything else. So then they try to reconstruct your past, which can be a challenge in it's own right when your memory is failing.
So now that you've gotten that far, they look at your symptoms and the order they appeared in, etc, and take a guess at what you have. The official diagnosis is "possible" or "probable" because the only way to be sure is a brain autopsy.
So yea you got 100 different symptoms, which can be anyone of about 80 different NDD's, oh yea and it isn't like this set of symptoms will mean you have "X" because every patient has a different set of symptoms even though they have the same disease. There is some distinction, like resting tremors is usually something on the Parkinson's Spectrum etc.
​​​​​​​It's just crazy, lol