Validated to the ceiling the publications allow.

Everything below is recorded in the adapter repository's VALIDATION.md and enforced by tests against the cached pinned run (upstream commit 846081a), so drift fails loudly rather than silently.

Since 2026-08-05 this comparison is an artifact, not a paragraph: define_uk.validation.baseline_calibration() recomputes every row from the cached pinned run against pinned external observations, the result is committed as validation/baseline_vs_external.csv, and the test suite fails on any drift between the committed table and a recomputation. Values use the annual-mean convention, so 2025 growth reads 4.66% where Table 4 prints 4.96% — the same −0.30pp anchoring gap recorded under the Table 4 gate.

external sources, row by row: ONS quarterly national accounts (uk_gdp_cvm vintage 2026-07-26; 2025 calendar-year mean over 2024) and OBR March 2026 EFO near-term 1–2%; OBR long-run growth assumption ≈1.5–1.8%; ONS MGSX (vintage 2026-07-26; 2025 annual mean, matching the model column's annual-mean convention); ONS 16+ population estimate; ONS labour force ≈34–35m; DESNZ UK territorial greenhouse gas emissions, 2024 provisional (2023 final: 384); UK NDC of 68% below 1990 by 2030 — the manual itself notes the current-policies baseline falls short by design.

The implication drives the product: near-term baseline levels are not competitive with the OBR emulator or the BoE SVAR and must never be presented as forecasts. The manual says the baseline “should not be seen as a prediction”; we take that literally. The defensible outputs are scenario deltas, with the demand-led caveat stated.

Our own computation of the model's cumulative green-public-investment multiplier — cumulative ΔGDP over cumulative ΔSPEND_GVT, nominal, over the full simulation — is 1.78. IMF estimates of green-spending multipliers run 1.1–1.5 (Batini et al. 2021); the OBR's capital-spending impact multiplier is ≈1.0. Above but near the IMF range, as the demand-led closure predicts, and labelled accordingly wherever a delta is served.

The upstream repository's own Multiplier_Summary.csv is documented unusable: its multiplier columns are identical across all eight scenarios, and its ΔG figure matches the cumulative delta of no variable in the scenario file. It is never quoted; a previously circulated ≈2.4 derived from it should not be either. Our computation supersedes it and is pinned in the test suite.

The one open divergence: the pinned upstream code runs below the manual's published Table 4 emissions, and the gap widens with horizon.

This is not an extraction error: the components (EMIS_NELEC + EMIS_ELEC) sum exactly to the total, and the baseline is identical across scenario folders — so it is a vintage or calibration gap between the published table and commit 846081a. The divergence is gated at the observed ratios so any further drift fails loudly, and it has been raised with the authors on the upstream issue tracker (DEFINE-model/DEFINE_UK_1.1#1).

What is verifiable is verified, at three levels. The design gate pins that each scenario toggles exactly its published policy switches. The oracle gates pin the delta paths against the cached pinned run — deltas finite, baselines identical across scenario blocks, sign sanity, eleven pinned delta points. And the two figures the paper's open 2023 conference vintage states in text both anchor, within deliberately wide vintage tolerances: green public investment peaks at +0.92% of GDP against a published ≈+1%, and the 2030 current-policies baseline emits 342.8 MtCO2e/yr against “just under 350”.

The upgrade path is equally explicit: the gate reopens if the authors publish scenario tables, or if the paywalled papers become accessible. Until then the status label stands — experimental; partial replication; scenario deltas only, never levels — and the score a reform workflow does not accept this model.