One year is counted from the time you did the medical exam to the time the IO will check it. My doctor said that some applicant's medical exam got expired (some vaccines were outdated) by the time the IO processed his case and he had to re-do it , even though he submitted it on time. Our vaccines are often with an expiration date far ahead in the future. If your doctor could re-sign the form to a current date, perhaps it's okay.