I don't know if this is the same person, but a M. Jouvencel's library was sold at auction in Lyon, July 26-August 26, 1779; it was a supplementary sale to that of Jean-Philibert Peysson de Bacot, whose name appears on the title page of the catalogue. In researching this sale, I was never able to find any biographical information on Jouvencel, not even a first name. The catalogue, which I know the Grolier Club owns, may list a copy of the book you have in hand, increasing the likelihood that this is the same collector. If this is the case, I would love to know- one may be able to trace the owner's full name by the arms on the bookplate...
Michael North, northm@mail.nlm.nih.gov
Rare Book Cataloger
National Library of Medicine
History of Medicine Division
8600 Rockville Pike
Bethesda, MD 20894
(301) 496-9204