What if at any 29th day of the month, the weather is always bad, so you can't observe anything, so that you always need to add a 30th day to the month
And what if at the contrary, you can always observe the moon at the 29th day and all your months are only 29 days
I think the second case can not be possible as the moon doesn't do a cycle every 29 day but 29,5 days, so you should be able to keep a good pace with the observation
But in the first case, their calendar will be late, their year will last longer
So is there any other system (than observing at the 29th day) to correct a bad weather in order to correct the calendar, to synchronize a way or another?
It's already difficult some months where all countries have difficulties not to be synchronized (in the same country people fight each-other to know when begin ramadhan), but over a year, it's impossible (12 day difference per year maximum, so a completely different calendar depending on the country)