How do we know the Kronos numbers are real?

You do not have to trust them. The reduced-order engines, inputs and expected outputs are deposited openly on Zenodo (CC BY 4.0). An independent reviewer can re-run them and reproduce the published figures — byte-exact for deterministic results, within tolerance otherwise.

The breeder's Q = 3.424 is backed by a 23-check validation suite; the burner's Q_E = 1.31 by a 45-check suite.