Grammaticalization is often considered to reflect frequent co-occurrence of certain elements in certain positions. This paper tests the frequency-based account of the grammaticalization of person agreement, comparing the grammaticalization of person agreement in Tabasaran, a Lezgic language, with the syntax of free pronouns in closely related Agul. Our assumption is that the situation in Agul, where person marking is not grammaticalized, approximately reflects a diachronic stage prior to the grammaticalization of person marking in closely related Tabasaran. We find little evidence in support of a frequency-based approach, at least when frequency is treated in terms of global frequencies. We do, however, identify a highly frequent verb that already in Agul appears to regularly associate with the pattern that has generalized to become person agreement in Tabasaran. We suggest specific information structural configurations associated with this verb, which have provided the impetus for the development. More generally, we show that while global measures of frequency may not yield the correct predictions, investigating the syntactic constructions associated with individual lexical items may be more revealing, and provide a more realistic model for reconstructing the paths of syntactic change involving the generalization of existing and quite local patterns.