Board Thread:General Discussion/@comment-80.44.114.235-20130830134916/@comment-6881629-20160209182156

Vilkas's Sword is just a Skyforge Steel Sword they have the same id code, so the quest probably cheats a bit (like Garry Damrau pointed out) and renames the item at some point. If you see a skyforged sword in his inventory try taking it and seeing if it renames itself or if it counts for the quest. Otherwise reload back a bit and try again, on PC try the command 132.178.9.19 gave (but you do need a quantity) -

player.additem 0009F25C 1