Puddinghead ,you have a most inappropriate moniker!
The device in question was not actually a slat or slot but a leading edge flap. These are visible on the lower wings in the drawing and could be hinged to effectively change the camber of the wing, primarily as an aid to lower approach and landing speeds. Unusually this device is also visible on the leading edge of the tailplane.
The mystery aircraft is indeed the C.S.L. 1
Designed by Roger
Courtois-Suffit along with Capitaine
Lescop the C.S.L.1 flew first in January 1918.
A very logical and well observed response, if I may say so.
Puddinghead you have control
Commiserations to S'land this time for being pipped at the post.