I was browsing diagrams offered by the merchant in Floatsam when found a weird bug. He was offering Diagram: Jagged Blade (damage 19-24). I didnt buy it, cancelled the trade window and opened it again. He was now offering Diagram: Jagged Blade, dmg 20-25.

Perhaps he was just trying to sweeten the deal!

Perhaps, but he cheated. I just crafted that sword and its damage is in fact 19-24.