Would it be wrong (in BrE) to say that when something was done but it wasn't necessary only "needn't have done" is used but it is not used for an action that wasn't done? For example, "I needn't have bought another loaf of bread. We already had one." (I bought it). If I didn't buy a loaf of bread or even if I bought it but it wasn't necessary I can use either "I didn't need to" and " didn't have to". Am I right?