First, Iowa and New Hampshire will be required by their State laws to move their events forward in the calendar.
Second, this is not an election required by State law. Each party has it’s own rules for who and when people will vote. The Iowa caucus will have no absentee or overseas military vote, because that’s not how a caucus works. New Hampshire may, or may not, depending on the way State Law works concerning party elections.
These laws are very well known and understood in all election circles, so Florida knew that it was accelerating the pace by making this move.
I understand ballots for military have to be printed and sent out before long especially Florida. This is probably more my concern since I have 5 active military and 4 will all be in Afghanistan soon.