Usage-based (UB) accounts conceive of language learning as continuous, locally contingent construction learning, i.e., a lifelong process of developing and honing the repertoire of constructional patterns geared to the optimization of a language user’s communicative ability across a wide range of language domains. The continuous nature of the process entails that a full UB model needs to account for not only the dynamics of language learning at early stages of acquisition, but also the functionally motivated adaptations of the language system at more advanced levels of proficiency. We present a design based on naturalistic second language (L2) written productions that sets out to reconstruct the states of constructional knowledge of advanced L2 learners through the statistical analysis of their productions. Irrespective of theoretical framing, the study provides foundational data relevant for any property theory of language learning, i.e., any theory that is concerned with the nature of the language system to be acquired, which logically precedes a transition theory of the developmental processes of L2 acquisition.