Be careful: The spin contribution to the number current is proportional to $\nabla \times S$ where $S$ is the spin density. The spin contribution to the momentum density is $(\nabla\times S)/2$ because the $g=2$ gyromagnetic ratio makes spin twice as effective at contributing to the number (electric) current as to the momentum density. See my contribution at "Gordon Decomposition""Gordon Decomposition" for more details.