The useful difference
QUAD keeps apart things that usually get blurred together. Holding value, proving work, moving between chains, and trading fast can cooperate without pretending they're the same kind of truth.
Each part shows what it can prove, what it can't, and what would change the answer.
A receipt, route, listing, balance, or feed means only what the part that owns it can back up.
Closed, stale, and refused are honest signals, not things to hide.
The four chains help each other without inheriting each other's authority.