Based on computations of Pandharipande (1999), Zinger (2011) proved that the Gopakumar–Vafa BPS invariants \mathrm{BPS}_{A,g}(X,\omega) for primitive Calabi–Yau classes and arbitrary Fano classes A on a symplectic 6 -manifold (X,\omega) agree with the signed count n_{A,g}(X,\omega) of embedded J -holomorphic curves representing A and of genus g for a generic almost complex structure J compatible with \omega . Zinger's proof of the invariance of n_{A,g}(X,\omega) is indirect, as it relies on Gromov–Witten theory. In this article we give a direct proof of the invariance of n_{A,g}(X,\omega) . Furthermore, we prove that n_{A,g}(X,\omega) = 0 for g \gg 1 , thus proving the Gopakumar–Vafa finiteness conjecture for primitive Calabi–Yau classes and arbitrary Fano classes.