Thank you for this nice piece of information.
One comment regarding the fact that the lounge is located outside the customs area. There are Skyteam long-haul flights arriving in other terminals (2A and 2F) so it is logical to have it accessible to passengers who have landed and passed through customs in another terminal. With the opening of Terminal 2E next year and the subsequent reorganization of AF operations, this might change in the future.
Regarding the fact that it is not displayed on any terminal map, I think the lounge is a very recent addition (January ?) and that the maps have not been updated accordingly.
Lastly, the C2 gate I was referring to is not the boarding gate but actually the gate for exiting the terminal building.
I am glad you enjoyed this new facility that I should be able to visit next month !