PHOENIX — More than 3,100 Maricopa County general-election ballots were mailed to voters on Oct. 1, six days before the scheduled start of ballot mailing, after an error by election services vendor Runbeck Election Services, county officials said. The premature mailing was not authorized by the Maricopa County Recorder’s Office. Officials said the ballots went to the correct voters and are valid, and recipients can fill them out and return them as usual. Early voting was scheduled to begin Wednesday, Oct. 7. Ballots returned before processing begins will be kept unopened in secure storage, then scanned and signature-verified with the regular batch, said Sam Stone, the Recorder’s Office chief of staff. “We did check with the Maricopa County Attorney. There is no reason voters should feel discomfort about the ballots,” Stone said. “They are valid. They are absolutely free to put them back in the mail immediately.” The Recorder’s Office said it planned to inspect Runbeck’s process beginning Monday, Oct. 5. Officials did not provide further details about what caused the error. Other voters were expected to receive their ballots after Oct. 7. Oct. 5 was also the deadline to register to vote in the November general election.