Nearly 98,000 people whose citizenship documents had not been confirmed can vote in state and local races, the Arizona supreme court has ruled.

The court’s decision comes after officials uncovered a database error that for two decades mistakenly designated the voters as having access to the full ballot. The voters already were entitled to cast ballots in federal races, including for president and Congress, regardless of how the court ruled.

The secretary of state, Adrian Fontes, a Democrat, and Stephen Richer, the Republican Maricopa County recorder, had disagreed on what status the voters should hold. Richer asked the high court to weigh in, saying Fontes had ignored state law by advising county officials to let affected voters cast full ballots.

Fontes said not allowing the voters who believed they had satisfied voting requirements access to the full ballot would raise equal protection and due process concerns.

The high court, which leans Republican, agreed with Fontes. It said county officials lack the authority to change the voters’ statuses because those voters registered long ago and had attested under the penalty of law that they are citizens. The justices also said the voters were not at fault for the database error and mentioned the little time left before the 5 November general election.

“We are unwilling on these facts to disenfranchise voters en masse from participating in state contests,” the chief justice, Ann Scott Timme, wrote in the ruling.

Of the nearly 98,000 affected voters, most of them reside in Maricopa County, which is home to Phoenix, and are longtime state residents who range in age from 45 to 60. About 37% of them are registered Republicans, about 27% are registered Democrats and the rest are independents or affiliated with minor parties.

Arizona is unique among states in that it requires voters to prove their citizenship to participate in local and state races. Voters can demonstrate citizenship by providing a driver’s licence or tribal ID number, or they can attach a copy of a birth certificate, passport or naturalisation documents.

Arizona considers drivers’ licences issued after October 1996 to be valid proof of citizenship. However, a system coding error marked nearly 98,000 voters who obtained licences before 1996– roughly 2.5% of all registered voters – as full-ballot voters, state officials said.

The error between the state’s voter registration database and the Motor Vehicle Division has since been resolved.

That number of votes could tip the scales in hotly contested races for the state Legislature, where Republicans hold a slim majority in both chambers.

Voters are also deciding on the constitutional right to abortion and on a state law that would criminalise non-citizens for entering Arizona through Mexico at any location other than a port of entry.

Though Richer and Fontes disagreed over the status of the voters, both celebrated the court’s ruling.

“Thank God,” Richer said on the social platform X. He told the Associated Press on Thursday that maintaining voters’ statuses would be administratively easier.

Fontes called the ruling a “significant victory for those whose fundamental right to vote was under scrutiny”. Election officials will be contacting voters who need to update their proof of citizenship after the election, he said.