Some time ago, the NZ government told INZ to set short deadlines, in the hope this would speed up processing. In practice, INZ COs know that people can't do magic and produce evidence in no time flat, especially if it involves getting an appointment, as in your present case. Therefore, if the applicant replies before the date stated, showing what they have done to provide what is required, they will normally be reasonable about it and allow the necessary time.
If I were in your place, I would reply so the CO will find it when she comes back, telling her that she has overlooked your new medical and X-ray, dated (whatever), and asking her to confirm if, now she knows there is a more recent one, she does require a new X-ray, also telling her you have not been able to get an immediate appointment.