There exist pisans in inventories all over the 14th century but no evidence specifically for rigid neck defense. This is why, although no artwork exists to confirm or deny, it is thought to be unlikely that rigid gorgets existed prior to Great Bascinets. Inventories are very detailed and heavily relied upon sources for the existence of certain pieces of equipment. A double layer of maille, each with its own layer of padding, as would exist with a pisan and aventail combination would provide pretty good protection, even from a thrust. You have to consider that most extant aventails are small rings, much smaller than the modern standard 9mm maille. So very small riveted rings, layer of padding, another layer of riveted rings, another layer of padding... that's good protection.
There's also a ton of artwork, specifically effigies that depict knights with no helmet on. Most French effigies are sans helmet (unlike English which almost always show the bascinet on the knight's head). The French effigies that do depict helmet-less knights either show no additional neck protection, or a maille pisan. So while there's is no smoking gun to say a rigid gorget didn't exist somewhere in the annals of the 14th century... it's extremely unlikely.
There's certainly nothing wrong with wearing rigid neck defense while doing combat sports for safety purposes. But it's unfair and a little bit disingenuous to try and call it 'historical' when nothing points to its existence. I would certainly consider wearing a rigid gorget for combat. I would just note that it is a safety compromise, and not try to claim its historicity for my chosen period. Remember, it's OK to do something ahistorical for safety purposes or for some other practical limitations, but don't try to 'force' something to be historical when there's no evidence that it was. That only serves to make the person wearing it feel better by saying it's historical, but it's not doing anyone any favors. So, there are two issues here. One is historicity, the other is safety. Don't try to force one in to the other if they don't already do that naturally, and always make note of that in a Living History demo if that particular item comes up in discussion. That being said, you could definitely get away with a steel gorget under an aventail. Especially something low profile like this (which is the one I would get if I were in the market):
(even though Erik is not doing custom work at the moment, I know he tries to keep these in stock)
http://www.wintertreecrafts.com/items/gorget.html 
