That’s the number the Secretary of State’s Office is reporting, according to the Inquirer’s excellent journalist covering these issues, Johnathan Lai.
That would not be 10,000 votes for Biden, of course. If these ballots broke the way other absentees in PA did, about 78% would be for Biden. But that percentage might not be right, because we have seen in some other states that late-arriving absentees broke more Republican than earlier ones. But using that 78% as a rough figure, that would mean Biden would net 5,600 votes from these ballots.
I am not sure whether the votes from these ballots are already included in the current PA vote totals or will soon be added to those totals. Either way, as many of us predicted in advance, the total is not significant compared to Biden’s margin in PA.