When dealing with medical absence, employees often notify their employer of the absence at the correct time. It's also common for an employer to receive a Medical Certificate from an employee a few days after the employee has been absent.
If an employer receives such a certificate and endeavours to reject it on the basis that the certificate is dated after the date on which the employee took leave, this would be unreasonable and considered a breach of Sections 107 (3) and (5) of the Fair Work Act.
Retrospectively-dated Medical Certificates, obviously created at a later date by the Medical Practitioner, can be relied upon by the employee as evidence to support a personal leave claim (which include what was previously known as "sick leave").
Consequently any attempt by an employer to base termination on the receipt of such a medical certificate is going to be fraught with danger for the employer and may result in a successful unfair dismissal claim.
Any misunderstanding in relation to such a medical certificate can of course be reduced if the medical practitioner has clear handwriting and terminology of the medical certificate and the employer ought to have an "Absence Management Plan" which has a clear procedure for determining any questionable absence from work, on a case by case basis.