Agreed, but it is also notable that hide and leather were often formed into a thick layered armours as well, perhaps even more often so than used as single thick pieces hardened by boiling or other treatment.
The following is a description of Chou Dynasty era layered hide armour, and this type of protection is mentioned as late as late Ming dynasty and early Qing Dynasty (by then being made of buffalo hide and possibly lacquered). Similar type of armour was also used by Native North Americans and Mongols, and a Greek Linothorax made out of leather would not have been too dissimilar (what material the Linothorax was most commonly made of is debated).
Both Thomas of Spalato and Marco Polo seem to have described the Mongol variety (of ox-hide) as being "very strong".
The kia made from the hide of the two-horned rhinoceros (si) consisted of seven layers; that made from the hide of the single-horned rhinoceros (se) consisted of six layers; and that made from a combination of both types of hide, consisted of five layers. As the two-horned rhinoceros was thought to live for a hundred years and the one-horned variety for two hundred years, armour from the hides was said to last for similar periods. Therefore, an armour made from a mixture of both would be expected to last for three hundred years.
To make a cuirass, a dummy torso was prepared and the hides weighted. Two piles equal in weight were allocated, one for the upper half and one for the lower. The hides were then cut and fitted to the dummy and the various layers placed on each other and then sewn at the edges. As far as one can judge, the finished cuirass was like a sleevless coat opening at the front-the upper half from neck to loins and the lower, forming a skirt, reaching to the knees. These Kia could be rolled up when not in use and stored in a case termed kao.
From
Oriental Armour by H.R. Robinson.
The wiki article below claims that the layered construction was used with the European padded jacks as well, though it doesn't seem to mention any kind of significant possibility that these armours would sometimes be made entirely from leather or hide. Ofc, it is my impression that leather and hide armours were far more common in eastern Eurasia than in western as primary means of protection, being more often of auxiliary nature in Europe (such as with the cuir-bouilli which, afaik, was mostly intended to be worn over mail when used as is, and possibly only used to face padded jacks when meant as primary means of protection).
http://en.wikipedia.org/wiki/GambesonI think all types of armour need to act akin to additional tissue layer if they currently do not do so. The "light" armours should simply form a much thicker layer, or even work as multiple layers (which might be easiest way to emulate them in game). I'm rather unsure as well on whether force is taken away from a blow as it passes through tissue layers or if the game simply randomizes penetration rolls. I'm actually guessing that the latter is the case currently.