The nonlinear dynamics of a semiconductor laser with coherent, as compared to incoherent, delayed optical feedback systems have been discussed and contrasted in prior research literature. Here, we report simulations of how the dynamics change as the coherence of the optical feedback is systematically varied from being coherent, through several levels of partial coherence, to incoherent. An increasing rate of phase disturbance is used to vary the coherence. An edge-emitting, 830 nm, Fabry–Perot semiconductor laser with a long external cavity is simulated. Following this study, consideration of prior and future experimental studies should include evaluation of where on the continuum of partial coherence the delayed optical feedback sits. The level of partial coherence is an important factor affecting the dynamics.