Last season I played was like 25 or something so it’s been awhile . I ended up finding a Primal Little Rogue. I thought perfect ! I have a basic Slanderer in my stash and the mats for my first crafted Primal. I’ll just pop that in and upgrade it to Primal for the set , one found Primal and one crafted… it gave me a crafted version of the same Little rogue after throwing the slanderer in there. So I’m assuming I just wasted those mats and screwed myself until I find more primals to salvage ? I did read up on this upgrading your own gear to Primal with one free craft but that was a hard lesson to learn having no idea it had the chance to roll one of the two weapons from the Istvan’s set. Kinda feel like just calling it quits after that debacle. 
- Little Rogue and The Slanderer are two completely different items of the 2-piece Istvan’s Paired Blades Set.
- D3 does not change an item into a completely different item. (Regardless of the Recipe).
- The only Cube Recipe that can change an item to a different one of the same Set is Skill of Nilfur. (And it will only do that for Sets that have more than 2 pieces).
Unless you video recorded your experience, we can only assume you had two Little Rogues to begin with. I would suggest you keep the better of the two Primal Swords you now have and salvage the other one. At least then you can recover 55 Primordial Ashes.
Finally, you can farm The Slanderer. A well rolled Ancient one could be better than a poorly rolled Primal one. And, if you’re lucky enough to find multiple Slanderers, you can Reforge the worst ones in hopes of getting a well-rolled Primal one. (If it means that much to you).
Whatever you decide, good luck and good hunting! 
5 Likes