Deploying a power grid controller in the field makes it susceptible to message losses caused by the inherent uncertainties and non-idealities of communication networks, especially when the control action is taken at a sub-second time-scale. We consider a centralized power grid controller that monitors and controls resources in real-time. The resources send advertisements that contain information about their state, and an estimation of their behavior in the time horizon when the control action is expected to be implemented. The controller uses this information to compute and issue setpoints that are thus only valid for this time horizon. An occasional loss of one or more advertisements might render the controller incapable of issuing valid setpoints. We introduce advertisements with a longer-term prediction interval, which are constantly sent along with the short-term ones, and can be used by the controller when it is missing information from some or all resources. We show the advantages of using such an approach on a controller that, by exploiting local resources flexibilities, performs frequency support on the CIGRE benchmark low-voltage microgrid.