If a doctor issues a retrospective certificate for an illness dated in the present, this is considered an act of professional misconduct. 

Lesson: A medical certificate under normal circumstances must be prospective in nature, from the date on which the patient was examined. This means that it may mention the expected period of absence from duty necessitated due to the patients ailment. There may be some medical conditions which enable the doctor to certify that a period of illness occurred before the date of examination. The circumstances need to be carefully considered by the medical practitioners before issuing a certificate which specifies a period of illness prior to the date of examination, especially in case of a patient with a minor short illness, which is not demonstrable on the date of examination. The practitioner must add supplementary remarks, where needed, to explain the circumstances that called for the issuance of certificate retrospective in nature, i.e., prior to the day of consultation (DMC/DC/F.14/Comp.647/2010)