One of the most convincing explanations papers generally provide concerning clusters in knowledge-based economies refers to the geographically bounded dimension of knowledge spillovers. Here, we shall underline that location decision externalities precede local knowledge spillovers in the explanation of cluster aggregate efficiency, which thus requires us to focus on the sequential process of location and the nature of interdependences in location decision-making. To that end, we mean to associate cluster emergence with the formation of locational norms, and to study the critical parameters of their stability. These parameters relate to the type of decision externalities among more or less cognitively distant firms, which influences the weight and the resulting ambivalent role of knowledge spillovers at the aggregate level of clusters. We suggest two theoretical propositions which we test within a simple and general norm location dynamics modeling framework. We then proceed to discuss the results so obtained by comparing them with an emerging related literature based on the life cycle and viability of clusters.