Behind the red coat or black hoodie they most of the time, they never use the actual actress/actor. They have used men in the past, like when Shanna shot Ezra, that built was manly but it was really Shanna. They do everything they can to throw you off. I think that Cece is A because you can tie her to almost any large event in the show since season 3 when she took back the A game from Mona who was exposed in season 2. One of the best theories that I've seen is that Charles and Cece loved each other and now Cece is the one playing Charles. Even the producer said that we would feel very sorry for A when we find out why A is A and that that it would be a romantic tragedy of sorts. The theory I believe is that Mona is under the black hoodie working double agent with red coat aka Cece aka 'charles' aka A and is using Charles as bait to expose Cece. It is possible that Alison unmasked Mona in the last episode.