The common US English meaning of date through date is that it ends at midnight (Pacific time specifically, which is 3 AM Eastern next day) of the day that is the last day. So through May 11th means just that, US time. How that works out in the other parts of the world, I do not know exactly. Thus, the confusion that regularly happens.
"No sadder words of tongue or pen are the words: 'Might have been'." -- John Greenleaf Whittier
"Do or do not. There is no try." -- Yoda
On planet Earth, there is a try.
Indeed, in a world and life full of change, the only constant is human nature (A is A, after all :P).
We old vets need to keep in mind those who come after us.