Conditions for the Validity of Physical Answer in Quantum Theory

Quantum theory has long been accompanied by disputes about what should count as a physically valid answer, yet the relevant standards have often been left mixed. A theory may answer every operationally meaningful question in a fixed experimental setting and still fail to determine what follows in a wider physical domain, or fail to preserve the same physical answer across admissible reformulations. This ambiguity matters because it destabilizes interpretation comparison, leaves the scope of no-go theorems partly underdescribed, and permits gauge-related sameness claims to be argued without a fixed criterion of answer identity. This paper closes that conceptual gap by separating three conditions that are often conflated: observational sufficiency, predictive sufficiency, and representational invariance. I formulate a metatheoretical framework in which the validity of physical answer is defined relative to a specified class of questions and a stated criterion of answer identity. Within that framework, I establish three formally closed non-implication results. The result is not a new interpretation of quantum mechanics. It is a sharper criterion for what any claim of physically valid answer must minimally specify.