(NewsNation) — More than a week after Election Day, officials are still making their way through votes in several races that remain uncalled. 

Voters are waiting in the lurch on House races in California and Alaska, and Pennsylvania’s Senate race has gone into an automatic recount due to the slim margin between the contenders. 

Each state has its own rules on ballot counting, which affects the speed of tabulations and release of results, leading to different lag times.

And even though most races have been called, these are unofficial results projected by media outlets and not certified by election officials. That process could take several more weeks depending on state deadlines. 

What’s the difference between called and certified races? 

The election results reported on election night are never the final, certified result. Instead, those are unofficial projections called by media outlets or local election officials after polls close. 

Decision Desk HQ, used by NewsNation, uses forecasting models to provide the probabilities of each candidate winning each state in the presidential election and accurate estimates of the probability of Republican and Democratic victories in individual House and Senate elections.

Local election officials will also aggregate data and report unofficial results for state and federal offices. 

However, these numbers are not officially certified, which means they are not final. 

Election certification refers to the process of “election officials attesting that the election results are a true and accurate accounting of all votes cast in a particular election,” according to the Elections Assistance Commission.

Certification of election results varies between states and sometimes even between local jurisdictions within a state depending on the contest being certified, according to the EAC.

After every valid vote has been included in the final results and all required processes have been completed, the election results will be certified.

States have different timelines for the certification.

What races still haven’t been called? 

Three House races in California and the single House seat that represents Alaska are still pending calls by Decision Desk HQ.

In California’s 45th Congressional District, Republican incumbent Michelle Steel leads Democratic challenger Derek Tran by just 236 votes out of more than 300,000 votes cast as of Friday afternoon, when 93% of votes were in.

In Central California, Republican incumbent John Duarte holds a two-point lead over Democrat Adam Gray in the 13th District with 84% of votes in.

The state’s 21st Congressional District is also yet to be called. Democratic incumbent Jim Costa is leading against Republican Michael Maher, a former FBI agent, by 3% — or 4,739 votes — according to Decision Desk HQ, with 78% of the vote in.

California is known for taking its time to count ballots. The state allows mail ballots to be counted if they are received up to seven days after Election Day, and it also sends mail ballots to all registered, active voters, which means its volume of mail ballots is much higher than other states, reported The New York Times. 

Mail-in ballots require additional verification steps where each must be opened individually, validated and processed. 

The state’s deadline to certify and submit election results is December 13.

Alaska’s ranked-choice voting system has contributed to the time it takes to tabulate results, which may still be a few more days. Ranked-choice voting allows voters to rank candidates by preference on their ballots.

As of Friday, Republican challenger Nick Begich has a three-point lead over Democratic incumbent Mary Peltola. Two other candidates account for about 5% of the vote in the race for Alaska’s single congressional district.

Alaska’s deadline for certification is November 30th. 

The U.S. Senate election in Pennsylvania between Democratic incumbent Bob Casey and Republican David McCormick is headed for a statewide recount, which will take days for results as the process starts over.

NewsNation/Decision Desk HQ called the race in favor of McCormick.

As of Friday, Casey received 48.54% of the vote with 3,364,650 votes, and McCormick had 48.8% with 3,388,453, according to the Department of State. 

Under state law, a 0.5% margin between opponents triggers a statewide recount. 

A noon deadline passed Wednesday for Casey to waive his right to a statewide recount, and Democratic Gov. Josh Shapiro’s top election official, Secretary of State Al Schmidt, a Republican, announced that preliminary results had triggered a legally required statewide recount.

By law, counties must begin the recount no later than Nov. 20 and must finish by noon on Nov. 26. The recount process largely involves running paper ballots through high-speed scanners, a process that former election officials say might not change the outcome by more than a few hundred votes.

NewsNation’s Rich Johnson and The Associated Press contributed to this story.