This is one of those little things that's a big deal. Unless this decision is overturned, it will shave points off the Philadelphia vote. The 3rd Circuit appeals court upheld a requirement for Pennsylvania voters to put accurate handwritten dates on the outside envelopes of their mail-in ballots, saying it does does not violate a civil rights law. Via the Philadelphia Inquirer:

A divided 3rd U.S. Circuit Court of Appeals ruled to uphold enforcement of the required date on return envelopes, a technical mandate that caused thousands of votes to be declared invalid in the 2022 election.

The total number is a small fraction of the large state's electorate, but the court's ruling puts additional attention on Pennsylvania's election procedures ahead of a presidential election in which its Electoral College votes are up for grabs.

A lower court judge had ruled in November that even without the proper dates, mail-in ballots should be counted if they are received in time. U.S. District Judge Susan Paradise Baxter said the envelope date is irrelevant in helping elections officials decide whether a ballot was received in time or if a voter is qualified.