[A] I wanted a copy of the letter, so I typed it twice. – You needn’t have typed it twice. You could have used a carbon; I walked up six flights of stairs. – You needn’t have walked up; you could have taken the lift; She stood in a queue to get an Underground ticket. – But she needn’t have stood in a queue. She could have got a ticket from the machine. [B] She shouldn’t have stood in a queue. She should have got tickets from the machine. She shouldn’t have stood in a queue, (It was wrong or foolish of her to stand in a queue). She needn’t have stood in a queue, (It was not necessary to do this, but she did it).
[A] needn’t + infinitivo de perfecto se combina con frecuencia con could + infinitivo de perfecto. [B] needn’t have y should have comparados: should o ought to podrían ser usados en lugar de need o could en todos los ejemplos de [A] arriba, pero existe una diferencia de significado: shouldn’t have (done) implica crítica, needn’t have (done) no implica crítica.]
A Practical English Grammar (A.J. Thomson & A.V. Martinet) 