Null objects, female leísmo, i.e., the use of the dative le/s used as direct object pronouns for female referents, and the OV pattern with new information are frequent in spoken Basque Spanish. These (morpho)syntactic phenomena are absent (or extremely limited) in non-contact Spanish varieties and have their equivalent in Basque. Therefore, these structures are said to have been induced by the long-standing contact between Basque and Spanish. I have explored these phenomena in a corpus of letters written by Basque- Spanish bilinguals during the 18th and 19th century, an important moment in the spread of Spanish to now bilingual areas due to literacy. These data have then been compared to those from personal letters written by Spanish monolinguals. I have performed descriptive and inferential statistical analyses, using IBM SPSS Statistics 22.0, and have also analysed the data qualitatively. Results show that variation is due to internal and external factors, caused by linguistic convergence mechanisms, similar to the processes of contact-induced grammatical replication.