Simulations of management plans generally aim to demonstrate the robustness of the plans to assumptions about population dynamics and fleet dynamics. Such modelling is characterized by specification of an operating model (OM) representing the underlying truth and a management procedure that mimics the process of acquiring knowledge, formulating management decisions, and implementing those decisions. We employ such a model to evaluate a management plan for North Sea flatfish proposed by the North Sea Regional Advisory Council in May 2005. Focus is on the construction and conditioning of OMs, key requirements for such simulations. We describe the process of setting up and validating OMs along with its effects on the ability to communicate the results to the stakeholders. We conclude that there is tension between the level of detail required by stakeholders and the level of detail that can be provided. In communicating the results of simulations, it is necessary to make very clear how OMs depend on past perceptions of stock dynamics.