A best guess at how the ballot stuffing operation worked:

They had the historical voting records to know who does not usually vote in any district. They had ordered enough extra absentee ballots for all of them and spent weeks filling them out beforehand.

They had real time access to the voter records and had the names and addresses of everyone who had not voted when the polls closed. They had enough people already in place to drive an absentee ballot out to each of them and get their signature on the envelope to make it "legal". If any electronic vote switching was done, they collected enough "legal" ballots to make up the difference.

That is why none of the independent reviews could find the fraud in the ballots. The ballots were from the same contractor as the real ones, and they had the manpower to go out and gather 80 million votes from 80 million living people. Who was the manpower? The Nation of Islam and Islamist immigrants, the Working Families Party and the old Soviet network, the Chinese Red Guards who oldfags might remember as the Jesse Jackson Rainbow PUSH Coalition, any other foreign power that wanted a part in it, and Mix Six leading them all. The fraud is that the entire system is operated by foreign agents who have been defrauding the American government and people for decades.