Tang’s dequantisation programme established that several quantum machine learning algorithms admit efficient classical simulation when given ℓ2-norm sample-and-query (SQ) access to their input data. The specific choice of ℓ2-norm sampling—rather than uniform, ℓ1, or any other sampling rule—has hitherto been justified operationally by its polynomial-time implementability, but not axiomatically. We show that ℓ2-norm SQ sampling is the unique sampling functional satisfying five natural operational axioms (normalisation and positivity, additivity under coarse-graining, noncontextuality, unitary covariance, and continuity). The proof is direct and does not invoke Gleason’s theorem.This note operates top-down: it begins from the standard quantum formalism (Hilbert spaces, unitaries, density operators) and works downward to show that the five axioms uniquely force the ℓ2-norm sampling rule at the Instrumental layer of the Unified Emergence of Information and Reality (UEIR) operational pipeline [15]. It therefore provides a strong contribution to Criterion #2 (axiomatic justification for the Born rule) and Criterion #3 (the classical shadow / SQ access rule is the unique classical implementation of Born-rule measurement) of the quantum reconstruction programme. It does not derive Hilbert-spacestructure from first principles (Criterion #1), which remains an open direction stated explicitly as Open Problem 2.The same five axioms underlie the operational derivations of the Born rule in quantum mechanics (Hardy [7]; Chiribella–D’Ariano–Perinotti [8]; Masanes–M¨uller [9]). Tang’s SQ access is therefore not a design choice but the unique classical implementation of Born-rulemeasurement.