Presumably the organisations responsible for hard coding backdoors in chip designs know how to test to confirm their presence.

Presumably some adversarial nation-states have moles inside these organisations > know how to remove them prior to fab.

Presumably these adversaries export genuine chips to their adversaries, thereby tricking them in to thinking the backdoors made it through the fab process, and only use chips that have the backdoors removed in their own critical infrastructure.

Presumably.

I’ve always had this fantasy of being a hextuple agent involved in this type of deep espionage.