The establishment of regional Parliaments in Western Europe has renewed the study of political careers. Since the beginning of the 21st century, an increasing number of – conceptual and empirical – studies have been published on political careers in multi-level systems. Despite the richness of the novel analytical approaches proposed, I argue that the current trend in the literature that consists to label a whole region (or even a country) as illustrations of integrated, alternative, or hierarchical careers pattern (might) produce an imperfect picture of the reality – or even worse, could lead to a misleading conclusion. I rather hypothesize that, within a single region, the possibility of multiple careers patterns has to be a priori considered: distinct professional political classes might co-exist. In this respect, two methodological elements must be integrated into the research design. Firstly, from a heuristic point of view, researchers should move from the (mere) analysis of level-hopping movements between two elections and rather adopt a microscopic point of view through the study of every single individual political careers (internal validity). Secondly, the cases under investigation should be selected only if they display a critical amount of legislatures in order to observe robust and non-contingent career patterns (external validity). For the sake of parsimony and clarity of my demonstration, I recourse to an in-depth case study – Walloon political careers – but cross-sectional research are certainly determinant to (in-)valid this hypothesis.