This cross-dialectal diachronic study focuses on actualization-the gradual mapping out of structural innovations across linguistic environments-and asks: to what extent can the route by which actualization unfolds be explained by appealing to common cognitive constraints, and to what extent are pathways of actualization shaped by community-specific patterns in language use? I analyze real-time syntactic change in Spanish oblique relative clauses (ORCs), which are undergoing an enhancive change towards increasing use of antecedent-agreeing definite articles (e.g., la casa en [la] que nací ‘the house in which I was born’). Over 8,000 occurrences of ORCs were compiled from three Latin American varieties. A Bayesian mixed-effects logistic regression analysis shows that various constraints representing the cognitive accessibility of the antecedent influence actualization similarly across varieties. The discussion addresses the cognitive realism of historical corpus data and formulates testable predictions that present profitable lines of inquiry in future cognitively oriented cross-dialectal diachronic research.