I just recently came across a KO Optimus Prime from someone who said it was original. Here are a few tips:

1. On the box, the date, and who made the toy (Hasbro,Takara) should be in black lettering, no matter if it's a decepticon or autobot box. It's always black, and not white lettering.

2. Optimus and the trailer cab have the Takara/Hasbro,made in Japan and date stamp. The cab especially should have some Japanese writing with the date and manufacturer stamp with a large "T" in side the slot where Optimus connects to the trailer cab while in big rig form. The inner leg Optimus is where the stamp should be on him.

3. If you look at the cardboard trim in the front of the box. A knock off will have the top trim missing. The cardboard trim should connect all around the front of the box around the clear plastic guard. Also, the styrafoam insert shouldn't be snow colored white or without any scratches if the item isn't factory sealed. Unless there was a humidifier used to preserve the toy, bright white styrofoam insert = knock and/or re-issue.

4. For any transformer, you should be able to see yellowed tape on the flaps and on the back where it was sealed. Come on, non-scotch tape doesn't look clear after 20 years oxidation.