Knives are a bit of a obsession with me, I originate from what the U.N. called the "stabbing capital of the developed world". Stabbings were (probably still are) a weekly occurrence (Friday and Saturday nights) and several of my acquaintances in student days were disfigured through incidents with knives.
One of the main reasons I started karate in the first place was the prevalence of the casual use of knives. It turns out that none of the training I did in the early years was of any use at all for self defence, never mind that of knives, but we don't know these things as beginners. In more recent times as I train I've been looking for a good, proven knife defence and found really just speculation, dubious techniques and lots of dire warnings from professionals with graphic photos. It seems that there is no such thing. It really doesn't exist under our current context.
However the other day as I was pouring over the medieval treatises and wondering why on earth all of the daggers were being used point down, not up as is most common today, it struck me that they had solved the problem. Or at least dealt with it. They didn't have just knives to worry about, but arming swords and other still larger types of sword. They already knew how to deal with knives.
The solution to blades it seems is armour. The daggers are most commonly used point down in ice-pick grip because generating enough force to punch through armour when using them point up is rather difficult. That's silly I hear you, that doesn't help at all. We can't all wander around every day wearing chain mail or plate mail armour. No, obviously we can't, but historically only the wealthiest could have afforded those types of armour anyway, your average soldier would have made do with something far cheaper and men-at-arms would have spent more time fighting ordinary soldiers than they would other plate armoured knights. The attacks documented in the treatises would have been most commonly used against the most common armour of the day. The Gambeson (aka padded Jack, Aketon).
A Gambeson is a type of armour made of fabric, not leather, chain or plate and used both under other types like the chain or plate and also as stand alone as armour in it's own right. It was simply multiple layers of linen quilted together; up to 30 layers. It turns out that fabrics in fact make good armour against blades particularly when layered.
A slash or cut from a sharp knife against bare flesh will slice it open in a deep wound with little resistance. Add a single layer of fabric like denim and the damage done to the flesh will be reduced. If you put 2 or preferably more layers of the fabric in front of the flesh the damage can be reduced to superficial wounding or eliminated entirely even for strong slashes or cuts from a sharp blade. What a few layers fabric won't do is prevent stabs from penetrating. In order to prevent stabs you need many layers of fabric more like the 20 layers in a gambeson using conventional fibres like linen. However even a few layers of fabric almost eliminates an entire attack vector from a short blade leaving just the uncovered areas vulnerable.
When you start getting up to 30 layers of fabric even stabbing someone with a sharp point becomes difficult. Sewing machine type knife attacks don't generate enough power to penetrate and the attacker must make a committed attempt to stab with body weight behind it to go through all the layers of cloth. Hence all the daggers in ice-pick grip. This is what a typical medieval gambeson would have looked like BTW. A bit bulky but really not much more than an average outdoor jacket.
For all of Fiore's medieval knife defence techniques which I have no reason to believe they don't work, I think there is a basic assumption that can validly be made about them. The practitioners would have been wearing some type of armour. The same is likely true of techniques taken from Asian systems like ju-jutsu. In fact historically when bladed weapons were involved at all, those involved usually made sure that they had armour on.
And that, is a crucial missing component of all of today's knife defence systems. In the current unarmoured context If you attempt to disarm someone with a knife you are attempting an extremely high risk task, if anything goes wrong you are up close and personal with the blade.
Today we have more appropriate fibres than linen, cotton or wool. We can do in a single layer what they need 10 or 20 layers of fabric. This is what modern fabric armour looks like:
We can make completely normal looking jackets, t-shirts or even under garments which are armour against blades. Not perfect armour by any means, there is no such thing but the point of armour is to reduce the attacker's effectiveness and options. The only thing which works now against the armour are committed thrusts. The other attack vectors have been closed.
For convenience the most useful design would probably be some kind of jacket liner, like a zip-in liner for common outdoor jackets. As well as zip-in insulating fleeces you could zip-in armour. It's something I would definitely consider for myself and family for every day use.
 Example cutting and stabbing tests using swords of various types against gambeson material: http://www.myarmoury.com/talk/viewtopic.php?t=11131
 Promo video of anti-slash fabric: https://www.youtube.com/watch?v=WRPy06ppL-4