Actually, the reference picture above has been taken by me during a troop in Paris near the "Galleries Lafayette". So far, it's the only reference picture I've seen showing the back of the tactical stock. So I modified my design to reflect that.
My point is, while we can't prove the movie prop has a smooth back, we can't prove either it has texture to it. However, we can prove that at least one promotional blaster has a smooth back. Which is better than nothing .
Now good luck with the sale Heston, blasters are looking great!