I can't improve the nightingale blade at all? Don't even have the option, it says on the wikia that their is a bug with the higher level version (it scaled when you get it depending on your level) that you can't improve it. It has 121 damage for me without any improvement, with improvement I think it would go way past 300. Pity that daggers don't benefit from fortify one hand enchantment, my daedric sword does more sneak damage than my daggers due to enchantments. But I was hoping to use the dagger, this is a bit annoying. Anyone had this bug or know how to fix it?

I can't upgrade mine past (Flawless) I don't think it's a bug, I just don't think you can upgrade it. I think if you were to be able to upgrade it, it would probably be the best sword in the game.

I think its a dagger, if its a sword then daedric swords are better. You would be able to upgrade it to legendary if you had enough smithing (you would need to use enchanted gear and +smithing potions). My point is that it doesn't even show up for me on the option to improve.

Ah your right, it is a sword, dam. Was hoping it was a dagger, guess its not that useful anyway then.