The issue becomes whether the government can make up and enforce certain parts of laws to unnecessarily raise the bar for voting, or just catch enough people making dumb mistakes to cut into their margins or discourage them from voting in the future.

Yes, the law says you "shall" sign and date your ballot. But did you know that the law also says that if you vote in person, you "shall" shut a privacy curtain or door behind you, and "shall" fold your ballot before handing it over to the poll workers to be stuck in the box to be counted? Have you ever voted at a polling place with cardboard screens instead of curtains, or stuck your ballot into a blank folder, or just turned it over without folding it? Should everyone who didn't shut a curtain or door, or fold their ballot have their vote disqualified, or does the privacy-preserving purpose of that rule have other methods of fulfillment that don't justify tossing all those votes? The language is the same as the date provision, but you have to look at the purpose of it and whether enforcement of that language is material to that purpose, if it has one.

That's the "materiality" argument that this case is making (it had been made before and was accepted by a federal appeals court, but got tossed out by SCOTUS on a technicality; the state's Supreme Court was short a judge and tied 3-3 on whether throwing out all these undated/wrongly-dated ballots violated federal civil rights) -- and the argument will be very important if any election in the state is close enough for these ballots to matter.