My assumption about layla tul qadr is that when Quran was revealed there might have been different happenings in the skies and the same happenings might occur on different odd nights of Ramadhan each year. It is just as if someone was born on 15th jan 1994 at 5p.m. when it was windy and it was full moon. The next year he will celebrate his birthday on 15th jan but not every situation will be same as it was a year before, it might be sunny now and the moon phase will be differendifferent so the day the man was born will never be same again in each of it's feature so.So we do not know the happenings of the skies, it is not measured by the happenings in the world or in terms of the worldly TIME. God Almighty has His own measurements. It is quiet possible that despite of having difference in day and night around the world the Night of Qadr falls on same day for everyone or it might be possible that it is different for different parts of the world or it is different every year. Lastly, I assume that the happenings that occured at the time of the sending of Quran to the world, happens on different dates in Ramadhan each year. The happenings in the sky are actually the Night of Qadr and those special happenings occured with the sending down of Quran, now each year Quran is not sent down but those happenings do occur for example handing major matters of the world to angels. This is what layla tul qadr is in my view that it is special because of two things one is: writing decree, sending down Quran. Quran has been completed but the decree is written every year on one of the odd nights of Ramadhan each year.