What I think -- and that was from watching some news on Mexican tv is that many there are more dead but these dead are "undocumented immigrants" --- because they were showing these trailer parks and the trailers that were still standing were very shabby and apparently these trailers were not tied down like Americans would generally do with their trailers. These might be the people least likely to listen to warnings to evacuate and maybe there would be a reason not to tell the numbers missing or dead yet.
Interesting (and sad).
Someone upthread said that there were rumors of that after Andrew, but the numbers never came out.
If that is true, we'll never know.