According to Article 195, paragraph (3) of the Law on Business Companies, an investor is entitled to dividend payment if he is on the shareholder list on the day the Shareholder Assembly decides that dividends will be paid out to the shareholders; the „record date“ is basically the date of the Shareholder Assembly.
Therefore it is not possible for the Exchange to define the ex-dividend date, as it cannot be known in advance if the Shareholder Assembly will in fact vote for a decision on dividend payment.