A large percentage of mail-in ballot rejections involve ballots that arrive late. And this year it’s particularly complicated because there are a number of states whose absentee ballot deadlines are still tied up in court. Wisconsin, for example, briefly switched from a receipt deadline to a postmark deadline (meaning, ballots postmarked by Nov. 3 could still be counted if they arrived within a week of Election Day). But that case has now been appealed to the Supreme Court, and there are similar cases pending in Arizona and Georgia.