Dark matter need not couple equally to protons and neutrons; relaxing that symmetry can move direct-detection limits by orders of magnitude. Earlier studies of isospin-violating dark matter worked in the zero-momentum limit; we extend the treatment to the full non-relativistic effective-field-theory (NREFT) basis and apply it to XENON1T, DarkSide-50, DEAP-3600, LZ and DarkSide-20k. The headline surprise: under the Standard-Model-gauge-invariant formulation of the canonical spin-dependent interaction, argon — a zero-spin nucleus — becomes competitive with xenon, illustrating how strongly target complementarity matters for interpretation.