We present a Boltzmann/Cobaya audit of the Distinction Engine Universe (DEU) as a discrete-substrate cosmology with a fixed graph-index amplitude closure. The central result is that the DEU CMB branch closes at the rational registry index AG = 41 40 = 1.025, not at the continuum-normalized value A = 1. A fixed-amplitude DEU audit shows that exact 41/40 is statistically indistinguishable from the measured posterior branch Aplanck = 1.02505, with log BF[41/40 − 1.025058] ≃ 0.07. The same exact branch is strongly separated from the continuum-normalized DEU branch, with a standard posterior-Laplace diagnostic log BF[41/40 − 1] ≃ 511.46, and a mean CMB χ2 gap of approximately 1017, dominated by the high-ℓ Planck TTTEEE lite sector. Thus the A = 1 branch is not a neutral DEU solution that happens to fit poorly; it is the wrong amplitude index for a discrete registry substrate. We interpret AG = 41/40 as an effective refractive index of the DEU graph vacuum: a one-unit discrete overhead on the 40-sector carrier boundary. In this reading, the conventional continuum normalization is misaligned with the discrete graph substrate, while the 41/40 branch expresses the amplitude closure required by the registry. The same clock/index architecture has late-time projections in the global Hubble mapping, BAO radial Jacobian, and supernova point-source propagation sectors. These are reported as cross-observable closure diagnostics, not as independent parameter additions. All chains, ledgers, audit scripts, checksums, and reproduction commands are provided for inspection.