I suspect that no one would dispute the Rabbs' Fringe-limbed Treefrog (Ecnomiohyla rabborum) is actually the world's rarest - though the Corroboree may be one of the rarest in the wild.
A mate of mine from Taronga Zoo has been involved in the captive rearing and release of hundreds of frogs and spawn into the wild, and reported just a couple for days ago they have found spawning in the wild from eggs they released three years ago.