This paper analyzes some of the factors accounting for dative agreement drop in 19th and 20th century Lapurdian writers. Following Fernández & Landa (2009), a distinction is made between cases where dative agreement is apparently optional and cases where it is either obligatory or impossible. After describing obligatory agreement with experiencer and possessive/interest datives, section 3 addresses the situation found in complex structures. 3.1 examines dative causees, whose complex syntactic and thematic properties account for some of the observed instanced of agreement drop. On the other hand, in 3.2 we concentrate on datives thematically associated with the predicate in an intransitive copulative structure. Their failure to agree can result from the same agreement dropping factors examined before, but also from the absence of theta-transfer to the light predicate. In section 3.3 we turn to the transitive light predicate egin.