User blog comment:MarkvA/Skyrim's Most Wanted Features and Fixes/@comment-170.140.105.2-20111205185838

Bug fix: the Nightingale Blade, if you receive it when you are level 50+, will be the strongest form of the blade possible. However, you cannot improve this version of the blade due to a bug that keeps it from showing up at the grindstone. I would love to see this fixed, because I was very dissappointed that I had an awesome sword that was far weaker than my other blades simply because I could not make it legendary.