President Trump was in the lead in Erie County after all in-person voting from November 3rd was recorded. Then, as the count continued of mail-in ballots, Joe Biden gradually gained on the President until he took over the lead. A USPS whistle blower in the Erie post office revealed to Project Veritas the postmaster had ordered the backdating of ballots received after the third to show a November 3rd postmark.
Mail-in ballots received up to 3 days after election day can be counted according to recent controversial changes made in PA, but they have to be postmarked by November 3rd, so the backdated ballots are actually ineligible for voting and cannot be legally counted.
You can see the video at the link below: