Elections officials in Arlington acknowledged Wednesday that the county’s electoral board accepted more than a dozen provisional ballots in which a voter’s name had been checked off mistakenly as already having voted, a discrepancy apparently chalked up to errors by poll workers.

Registrar Linda Lindberg said a new system using bar codes this year might have confused poll workers and caused IDs to be scanned more than once. She said officials in the heavily Democratic county are looking more specifically into the source of the issue.

The uncertainty over a reported 17 ballots — ordinarily a minor anomaly in a race in which 2.2 million ballots have been cast statewide — takes on added significance in a Virginia attorney general’s race in which just 164 votes separate the two candidates.

With all jurisdictions reporting results by the midnight Tuesday deadline, the State Board of Elections said Wednesday that Democrat Mark R. Herring took 1,103,777 votes compared with 1,103,613 for Republican Mark D. Obenshain. Mr. Herring declared victory, leading to posturing from both campaigns.