This paper describes the results of an investigation into requirements discovery during testing and operations. Requirements discovery includes both new requirements and new knowledge regarding existing requirements. Analysis of anomaly reports shows that many of the anomalies that occur during these phases involve requirements discovery. Previous work by the authors identified four common mechanisms for requirements discovery and resolution during testing. The results reported here extend that work in two ways: (1) to show that very similar requirements discovery mechanisms are at work in both testing and operations, and (2) to evaluate the requirements discovery mechanisms against experience with seven additional systems. The paper discusses the consequences of these classifications and results in terms of reducing requirements-based defects in critical, embedded systems.