MP: Thanks for your question! Happy to explain.

According to the PA Department of State, every county is expected to include undated ballots in their official returns for the Nov. 8 election, consistent with the Department of State's guidance. That guidance followed the most recent ruling of the Pennsylvania Commonwealth Court holding that both Pennsylvania and federal law prohibit excluding legal votes because the voter omitted an irrelevant date on the ballot return envelope.
The order from the U.S. Supreme Court vacating the Third Circuit's decision on mootness grounds was not based on the merits of the issue and does not affect the prior decision of Commonwealth Court in any way. It provides no justification for counties to exclude ballots based on a minor omission, and the PA Dept of State expects that counties will continue to comply with their obligation to count all legal votes.