I have shipped a lot of single sheet letters by both FEDEX and UPS and always know where they are simply by checking tracking on the Internet. If the government really wanted to know where these 11 going on 30 million people are, they could find them. I would suspect that a good chunk of them are in California.
They could end the drought overnight. One third fewer flushes, and no one to fill the pools or water the lawns of the celebrities.