We didn't have three carriers during the Falklands War, we had two: Invincible and Hermes. Illustrious and Ark Royal did not enter service until after the Falklands War.
That much depends on when you think the Falklands war started and when it finished. There were 3 Carriers in the TEZ in 1982. HMS Hermes, HMS Invincible and HMS Illustrious.