“As stated above, sometimes special cash dividends make up a large percentage of a stock’s price. Many times this means that these large special dividends are applied with certain rules that differentiate them from normal dividends. The biggest difference concerning special dividend stocks is that the ex-dividend (for special payouts) comes after the record and pay date, not before (like is the case with regular dividends or smaller special dividends).
This difference occurs because on the ex-dividend date the stock exchange adjusts the stock price to account for the dividend to be paid out. If this same procedure were to happen in the case for a large dividend, say 25% of the stock price or more, then this might signal a huge drop in share price that could affect many traders and investors.
Rather than deal with these headaches, the stock exchanges apply a special rule to deal with these large one-time dividends. The exchanges (not the companies) set an ex-dividend after the record and pay date. Now, you may be wondering how some might receive their dividend if it is paid before the ex-dividend date (the date on which owners of a stock have the right to receive the dividend). To get around this obstacle, the stocks bought or sold in the period from the record date to the ex-dividend date (the due bill period) are tagged with something called a “due bill.””

For Gnbt this doesn’t apply. Fwiw, jmho,