What is this RK05 style pack?

A couple months ago I acquired a new, still in the plastic wrap, still in the box, never opened disk pack that at first glance appeared to be an RK05. I finally decided to look further at it to see if it was a 12 sector or 16 sector RK05 pack, since it had no identifying label or markings. Upon further inspection, I found that it did not have the usual rim on the hub, where normally you would be able to count the thin notches to determine whether it was a 16 sector or 12 sector RK05. Instead, it has a short, rounded, unnotched rim where normally it would have the tall thin rim with notches. Otherwise it looks just like an RK05. The case is interchangeable. I actually took it apart so I could use the case on another RK05 pack that had a decent platter but a bad outer case. What is this thing? RK03? Ashley