Mark/Laurent
Lucien Morareau agrees with Laurent regarding the unit.
AC5 was created on 20 June 1940 from teachers and pupils of the Fighter School at Hourtin (Cours de chasse). It certainly was in action since some recorded incidents happened already the same day it was formed.
The French Navy did not (perhaps surprisingly) have any system for victories, so there is no official list or anything you can rely on, which means all details published must have been pieced together from other sources.
In an earlier work Morareau does not list any Aeronautique Navale claims after 15 June 1940. Possibly because he did not at that time have anything reliable on the Cours de chasse. However in his later work he does mention that the unit was in action on 17 June 1940 to protect 'Jean Bart' when it departed Saint-Nazaire. No claims were made that day.
However on the 19th (as Mark also states) he notes a damaged claim by one of the intercepting Morane 406s over a He 111, but no name listed. Since my French is what it is (
), I am not quite sure if he means if the He 111 was abandoned by its crew or if the chase was abandoned by the French fighters.
I don't know where Gillet has found his evidence regarding the date 17 June but if I have to make a choice I would say the date 19 June is the more reliable. I have great faith in Lucien Morareau and his work. But again there is no official data to rely on here!
Cheers
Stig