As Moose4 has been explaining on various VA/Allen threads, (or at least as I understand it) each Congressional District has a 'special' precinct for provisional or conditional votes. Those would be the ones not yet counted, but it could also be that certain districts don't have any provisional ballots. They may incorporate military votes not yet in .. the military are given a few days to get their votes in after the election.
Earlier I heard 1900 votes had been applied to the Webb column that were supposed to be for Allen, which is a good sized swing. Not enough to make up the difference, so Allen & Co. are probably praying for a few more improperly applied entries.