Board Thread:General Discussion/@comment-186.136.41.156-20130704011652/@comment-6881629-20130718203038

There is a bug where you get a iron weapon in stead of the Blade of the Rift (which can also be a dagger). Finishing the civil war for the Imperials before becoming Thane can mess it up too, if your on PC -

Player.setstage FreeformRiftenThane 200

That should (after while) make the Thane option appear.