I think there is an error in both the CBS and CNN county by county tallies (and if the statewide totals are the sum of the counties, the error flows through to the bottom line)
Isle of Wight is showing 12 of 13 precincts with 5050 votes for Webb and 6984 for Allen at the Virginia interactive website.
CBS and CNN are both showing 9,050 votes for Webb. Checking the vote totals for the other county races, the correct number is almost certainly 5,050 - unless 4,000 voters went into the booth and voted for Webb and failed to vote for congress and the statewide ballot question
Bottom line - the Allen margin may be 4,000 votes higher than CNN and CBS are showing
or stuffed?