i would think that fretted fiddles would be viols which were a different family of stringed instruments that looked something like the violin but were gradually replaced when the Italian violin became popular in the 17th century. They had frets, and a sloping shoulder rather like the bass which by the way is the last descendant (so to speak) of the viol family.

The movie Tout les matins du Monde (all the mornings of the world) featured this instrument although it was the cello version.

anyway Im not an expert by any means. Petr