of course there are the ILLEGALS that we have no record of...
There are GPS records of everybody on both islands that were very active right up until Ike struck.
GPS cell phone records. If you were any of the large telecoms, you could query your customer database for those sending signal from the coord box of the predicted landfall.
Then look at those records after landfall, and those that have no activity 4 or 5 days later are likely never going to again.