I don't know if this just happen to me or if anyone else had this happen but I'm able to do the quest again and again.

I did the quest like your supposed to. I killed Forsworn Briarheart and got the Red Eagles Fury and upgraded it to the Red Eagles Bane.
I went back to the his dead body and I saw a book I read the book and it gave me the quest again.
I was thinking there's no way I can do the quest again, I killed the guy and I have the sword. I went back to the body and searched it and he had the Red Eagles Fury on him.
Long story short I was able to keep getting Red Eagles Fury swords but I could not upgrade them to the Red Eagles Bane.

Has anyone else had this happen?