Nd(Fe,Mo)12 compounds have been considered as promising candidates for next generation permanent magnet materials, thanks to their excellent intrinsic hard magnetic properties, comparable to those of the well-known NdFeB magnets, allowing a minimum usage of rare earth elements (RE). However, achieving high coercivity in an anisotropic microstructure has proven to be a significant challenge, which hinders their practical applications. In this work we present microstructural studies of the strip-cast Nd(Fe,Mo)12-based alloy. Detailed microstructural characterization using high resolution transmission electron microscopy (TEM) reveals sub-micron sized 1-12 magnetic grains, indicating that the addition of Cu leads to grain boundaries segregated into RE and Cu. Micromagnetic simulations based on the observed microstructure emphasize the role of grain boundaries and of crystalline defects on the development of coercivity. This work provides evidence about relevant aspects of the microstructure of these compounds that is correlated to the coercivity development.