On a genuine Rolex Twinlock, the two dots under the coronet denote white gold, while the single dot means platinum. Steel and yellow gold get the straight line. There's a good chart available if you Google Image Search "rolex crowns".
It looks like all the DD reps have single-line crowns, while all the DD2 reps have double-dot crowns. Most likely, the rep manufacturers used a WG model as the template for the latter.
I wouldn't worry too much about it. Anyone who notices the wrong crown probably already knows that the case isn't made of WG or platinum.