I don't understand. Is this correct that the Toy Boxes are not forward compatible? According to the Infinity Compatibility Guide, any Toy Boxes created in previous versions will carry forward, items and all.
Couldn't they make this any more confusing?
Yeah, the graphic is only referring to physical objects -- so, it's referring to the Toy Box Game Discs. Every digital toy you unlocked to create things in the toy box mode carries over.
The reason they're called Toy Box Discs is because those are the games where you can mix & match characters from different properties -- like Pixar & Star Wars.