Dear History of Medieval list,
Research has now revealed that the Ischia Manuscript MS408 is written in Graeco-Iberian language and uses a pronuncial writing system. All is explained in this paper: https://www.academia.edu/49263562/Voicing_the_Voynich_The_Pronuncial_Writing_System_and_Graeco_Iberian_Language_of_MS408_Ischia_Voynich_
The manuscript provides a wealth of information about the islanders of Ischia in the Medieval context, so it should be a useful resource for historians in that field.
Dr. G. Cheshire.