And yet no one challenged the law until after the third election it had taken effect. Until after the results had come out. There's a doctrine called laches: you have to complain about things that wrong you when you find about them, and if you wait too long, you don't get to complain anymore.
Furthermore, as for election challenges go, you're not going to invalidate any votes that had already been validly cast under the existing interpretation of law, even if the interpretation is incorrect per court rulings. For example, when there were last-minute challenges to absentee ballot procedures, any absentee ballots cast before the decision came out under the old procedures would still be valid, even if they didn't meet the new procedural requirements.
So anyone thinking that courts would invalidate election results via after-the-fact court challenges is either ignorant, lying to themselves, or is stuck somewhere in la-la land.