I am guessing. I would think that prior to the Wrights, early manufacturers would have used a flat surface as an airfoil. By definition symmetrical, but only due to lack of test or inspiration perhaps. Technically, Lilienthal employed flexible canvas wings?? Also technically symmetrical. The Rogallo comes to mind, I owned a Manta, it certainly was symmetrically airfoiled. For all his fame, Bernoulli predated all wings, his data was applied, and linked to fluid research.
The first Boomerang was perhaps flat, to be updated by a bright hunter in the outback
Some old guys may remember the 'Thermic50', or the junior 'Ringmaster' ?
bear