This study systematically evaluated 284 model chemistries, spanning semiempirical approaches, density functional theory, wave function theory, and composite methods, to compute standard enthalpies of formation (∆H • f ) for a 421-species training set. Both Petersson-type and Melius-type bond-additivity corrections, previously shown to improve ∆H • f calculations, consistently enhanced accuracy across nearly all methods tested. Nonetheless, species underrepresented in the training set (e.g., ions, triplets) saw smaller gains, highlighting the need for more extensive high-fidelity reference data in these areas.