Are you loading your mod in an existing save? Trade treasure is saved in your save file, so when you update your mod and load the existing save it will load the old (saved) trade treasures.
You can get around this by disabling your mod, loading a save, saving, and re-enabling the mod. Though, as far as I can tell this will also remove everything else which isn't vanilla.
Also make sure you let the trader restock their inventory. That happens every real-time hour since the last restock or after you leveled up. To make it easier for testing, just create a save when this condition is met and you haven't talked to that NPC yet. In the editor you can just point on your dummy character and press CTRL+SHIFT+L, that will level you up, hence refresh the trader.
