[A] You needen’t have watered the flowers, for it is going to rain, (You wasted your time); You needn’t have written such a long essay. The teacher only asked for 300 words, and you have written 600; He needn’t have bought such a large house. His wife would have been quite happy in a cottage, (waste of money); You needn’t have carried all these parcels yourself. The shop would have delivered them if you had asked them. [A 2] I didn’t have to translate it for him for he understands Dutch; I didn’t have to cut the grass myself. My brother did it. (no hubo obligación y no hubo acción). «You didn’t ‘have to give him my name» («It wasn’t necessary to give him my name, but you gave it to him»). You needn’t have given him my name.
[[A] needn’t have done: no había obligación, pero la acción innecesaria fue llevada a cabo, i.e. tiempo perdido. [B] didn’t have/need to do: no hubo obligación y, en consecuencia, tampoco la acción fue llavada a cabo. Hay hablantes que usan didn’t have to/didn’t need to y se refieren a acciones llevadas a cabo. El have o need es entonces acentuado. «You didn’t ‘have to give him my name» significaría entonces: «It wasn’t necessary to give him my name, but you gave it to him.» Al estudiante se le aconseja usar needn’t have + participio de pasado cuando una acción innecesaria se llevó a cabo.]
A Practical English Grammar (A.J. Thomson & A.V. Martinet) 