With the proliferation of scheduling algorithms there is a growing need to test these schedulers for their validity not just at design time but also as the system evolves. This implies that the schedulability analysis has to be robust. In this study, we identify a few often posed questions that address the robustness of schedulability analyses. First these questions are dealt in the context of uniprocessor systems and then we handle some of their extensions in a more general context of end-to-end systems. We show that these questions are closely related to a more general problem. We present a solution to this problem. An intuitive proof of correctness and optimality of the solution technique are presented.