To put it into context. Other materials were uses as well such as bone, leather, and wood. Anything that I can put in between my enemy's blade and my skin is going to be looked at as an option as long as it wasn't detrimental to my fighting ability. While a "thick coat" may not protect against a stab, it would still offer some protection against a slice or a blunt impact, and some arrows, especially if the cloth was woven. Even if it doesn't stop the arrow from piercing your flesh, it will prevent it from being a deep flesh wound. Ancient Armor made from paper.
Many years ago as a teenager, I was swinging on a rope next to a fence that looked like this. I had a thick coat one that had a pull up collar. I had the coat on because it the rope, which was thin, was cutting me. On one swing the rope snapped and the back of my neck landed on the the fence. Had I not had the coat with the high collar on then fence would have ripped the back of my neck and probably would have either killed me. My neck literally landed on the fence and I slid off the fence and landed on my feet. I didn't realize how blessed I was until I got in to the house. The fence put a 6 inch rip into the collar and ripped through all of the fabric except the wool on the inside. I've ripped my hand open as a kid before so I know from experience how fences like this will tear through flesh. Blades are like that when it comes to slashing. I'm better off with a thick piece of fabric between me and my skin. Don't think so. Take a towel, fold it twice and wrap it around a wood post. Then take a knife and try to slash the wood through the towel.