From my understanding when they called PA for Trump he was leading by 76K votes. They could call it because they knew there was less than 76K votes in absentee ballots.
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Correct except he was leading by 68,000 votes and then 70,000. After the provisional and absentee ballots which were already know but not yet counted the total margin dropped to 46,000 (Philly only) there were a few districts outside Philly which also finished up and since PA is fairly conservative outside Philly the total went back to about 49,000 where it is now.
There are not enough absentee or provisional ballots left to count to alter the results.This according to a PA voting official.