Nonlinear Compton scattering is one of the dominant processes in future ultra-short ultra-intense laser-matter interactions. Today, most related researches are based on the mainstream model of nonlinear Compton scattering, which assumes short radiation formation interval, ignores effects of involved laser photon energy and is not spin-resolved. To depict nonlinear Compton scattering more precisely in wider parameter space, improved theories beyond these assumptions have been proposed in recent years. In this paper, we reviewe the major recent improvements, analyze their applicability, discusse their basic characteristics and physical effects on nonlinear Compton scatterings.