That was because Allegheny County had just finished counting its absentee ballots after 100% of the election-day ballots had been counted.
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1) PA GOP/Saccone looking said to be filing multiple challenges, involving GOP people turned away from polls (told "you're not in this district"), votes changed in Allegheny, wrong info about voting day posted on SoS website and non-citizens voting.
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Those were the absentee ballots that caused the change.