You can still do it

From yesterday's Greek daily paper Kathemerini.

Thousands of people who own illegally constructed homes have applied to legalize their properties in recent weeks. Failure to do so would cost them the right to pass on the property to others unless they pay much higher fines, as foreseen by the law. In contrast, the fees charged under the current amnesty program, which is set to continue until the end of February, are considerably lower.

If anyone still has a property where there are illegalities - anything from just a 'closed in' balcony to much larger anomalies, people can still apply to legalise their properties. If they do not they run the risk of much larger fines, or the possibility of not being able to sell their property on, or even pass on as an inheritance, so it really is important to obtain advice on this from a civil engineer or lawyer.
Diana