Very speculative, specially Corretja when there are better onehanders around in this generation that cant get the job done.
Nadal won a set against Corretja when he was only 16 in Barcelona and he defeated Costa in straights in Monte Carlo.
So you think every one-hander before current era was worse than todays? Best one-handed backhands are from previous eras, but speculating their success against Nadal´s forehand is rather pointless, since Nadal´s heavy spin is made possible by todays equipment, and previous eras didn´t face that kind of shots.
As for Corretja, he was way past his prime by the time he played Nadal.