How the heck do they know any vote count until the votes are actually COUNTED? Am I missing something?
Yes. You are missing the process. Voters are on a roll with their registration noted. When they have voted or turned in an absentee ballot, it’s fairly simple to determine if more republican than democrat registrants have already voted.
And, probability says those folks will tend to stay with their party they are registered under.
More to the point, the votes haven't even been cast yet, let alone counted.
Florida early voting starts today.