Instantiating No External Model Selection in Physics Macroscopic Records, Non-Categoricity, and a Criterion for Class IIb

We instantiate the No External Model Selection Theorem in a physics-grounded setting by fixing an observational fragment based on stable macroscopic records. Building on the universality-class classification of realized systems under single actuality, no external model selection, and no free completion bits, we provide explicit sufficient conditions under which a realized universe must lie in Class IIb relative to the record language: observational multiplicity forces internal selection, and diagonal-capable self-reference on the same record fragment forbids total effective selection. The paper contributes (i) a minimal, operational definition of a record language and its record-truth semantics; (ii) a minimality theorem showing that captures the weakest standard observational commitments needed for empirical science; (iii) two complementary routes to establishing record-level non-categoricity in physically universal systems; and (iv) a theorem package separating a core Class IIb criterion from domain-specific premises that imply its hypotheses. The result is a conditional but sharp classification statement about the semantic architecture required of any closed, definite, computationally universal physical world. Trust boundary. Class IIb claims are conditional on the record-language and computability premises of this paper; the classification engine itself is in Paper 2, with formal companions in nems-lean. See.