As I understand there have been 3 molds in addition to the X mold. There was the original, which made the first run Tee-rexes and then the first run or so of Teerexes. Then that one broke. The one they made next is known as the "bad" mold piece (top). It made Teerexes, Vikings, and perhaps other discs that were less stable than intended. Last year they made a new top to replace the "bad" top and supposedly it started producing stable Teerexes again. What's more is there is no easy way if any to tell all of these apart when you are looking at the discs, except I don't think the original mold had the WWW.INNOVADISCS.COM engraving.