Validated 12-site conventional Fe₂B reference reconstructed from Materials Project mp-1915 CIF (ICSD 42530 provenance). Round-trip checks: Fe2B, I4/mcm #140 at symprec 0.01–0.1, a=5.063814 Å, c=4.236362 Å, Z=4, ρ=7.490 g cm⁻³, minimum pair distance 2.118 Å. Intended matched DFT-relax control.