Under a superset-based approach to spellout (Caha 2009; Starke 2009), a vocabulary item characterizes a set of PF-legible syntactic objects. The consequence is a dynamic, configurational and vocabulary-driven notion of a feature’s (un)interpretability at PF, that gives rise to the possibility of spellout-driven movement (Starke 2018). In this case study, I employ this to reinterpret Kouneli’s (2021) analysis of the tripartite number-based system of nominal classification found in Kipsigis. While Kouneli’s analysis makes use of uninterpretable classificatory features to derive the classes, I derive the classes from the restrictions on PF-legibility imposed the vocabulary items themselves, thus providing an explanatory account of the PF-legibility of particular number properties from a general theory of PF interpretation. This account also solves the issue raised by Alexiadou & Müller (2008) who show that introducing declension class feature in the syntax or at PF are both problematic for the Y-model. Since the proposal I argue for here disbands such features in favor of a configurational analysis of noun class, it shows the potential for resolving a serious conceptual issue.