Small-angle neutron scattering (SANS) in self-organizing nanostructured Fe1-xCrx (x = 0.21, 0.43 and 0.53) alloys has been studied. The relation between the nuclear and magnetic contributions depends on the alloy composition and the extent of self-organizing due to the demixing of Fe and Cr. When the demixing is pronounced with a large concentration fluctuation amplitude, the two scattering contributions are very similar, whereas when the concentration fluctuation amplitude is very small, the magnetic contribution is negligible compared to the nuclear contribution. The relation between the scattering signals is critical when assessing the demixing in Fe1-xCrx alloys by SANS, which has been mostly ignored in prior works in the literature.