Just to add to the conversation, you may also may wish to examine the changes due to advances in weaponry through out history. If those with money were the soldiers they would become a major driving force in inovation. As they (weapons) advanced, so would the armor worn. As weapons and materials moved from stick and stones, to clubs, to spears, swords then bows and arrows to cross bows etc. I think it was the chineese that even came up with an early version of bullet (arrow) resistant armor by utilizing overlaping layers of compressed paper and\or silk on the exterior of their armor.
Our saving grace is two fold. First the internet and sites like this one. Second is a paradigm shift from hording knowledge (aka Trade Guilds) where only those within the guild\group were privy to the "secrets" to sharing knowledge. Sites like this facilitate the dispersion of ideas, knowledge and techniques both old and new. Information and innovations that would\may have taken weeks to months to years to propogate across medieval europe now occur at the speed of light. The other is all your willingness to share your knowledge. Without that willingness to basically share with what could ostensibly be consideered your "competition" is truely a relatively new phenomenon.
PS Being a novice leather worker, I for one truely appreciate the access to your knowledge and experience