Today, I learnt that the last gamba built in France was an eight string instrument made by Benoist Fleury in 1759 (or 1769 depending on how you interpret the label) - right around the time the cello was gaining prominence. A copy of it can be heard in a new recording of Rameau's Pieces de Clavecin en concert played by Ensemble Fleury. I was thinking about Louis Guersan and his pardessus viols  and thought I saw somewhere an instrument dated 1770.