If you had actually read your article from this unknown source, it explains that California election law that passed several years ago, allows all 40 million Californians that are registered to vote, can vote via absentee ballot, which takes much longer to count because of the manual process of envelopes being opened and verification process etc...
AND California election law accepts all ballots mailed and dated on election day, and gives one week for them to arrive to be counted...so Nov 12th they begin counting all of the mail in ballots.
California election certification must be completed by December 7 under their laws....
....nearly every state has a different certification date. As example Florida vote count must be finalized and certified by November 19, my state is November 25.