The story of Innova's 3 molds as told by wims (fan fiction).
Innova buys a few new injection molding machines to keep up with the increased demand. The new machines have a different interface with the molds, so molds would have to be rebuilt. The new mold maker is using a different way of running coolant through the mold. This cause the discs to cool more consistent, and it also causes discs to mold up flatter.
When Innova discovered that their new Leopard / Roc / Teebird mold created flatter discs they immediately saw the marketing potential. Why not sell these discs as "Teebird 3", extra flat Teebirds?
When you look at the tooling on the bottom of the flight plate you will see that all lettering except for '3' is sticking out of the disc. It's sticking out of the disc because the text was engraved on the mold when the mold was produced. The fact that the number '3' is not sticking out, but rather sink in is evidence that the '3' number was added at a later time. In fact, '3' is not a part of the mold itself, it's stamped on the disc after the disc was produced. This is what is causing it to be indented rather than sticking out. If Innova had intended that these molds were '3' series molds when they were produced then the '3' would be raised as well, like the rest of the text on the disc
TLDR; Innova ordered new molds, discs produced by these molds molded up flatter than discs produced with the old molds. Innova took advantage and sold and marketed them as new discs.