Vector portal dark matter models, where dark matter couples to a dark photon that kinetically mixes with the visible photon, have become a widely-used benchmark for light sub-GeV dark matter in recent years. In particular, the regime where the dark photon mass is 1-2x the dark matter mass is characterized by a rich freezeout phenomenology, with three-body annihilation and kinematically suppressed processes potentially playing important roles. I will describe new research exploring the full range of possible thermal freezeout histories in this region of parameter space, discarding the usual assumption that the dark and visible sectors remain at the same temperature throughout freezeout. I will present calculations of the constraints on this scenario for both Dirac and pseudo-Dirac dark matter, and identify open regions of parameter space that are promising targets for future experimental searches.