One of the most heavily contested voting-policy issues in the 2020 election, in both the courts and the political arena, was the deadline for returning absentee ballots.

The policy in a majority of states was that ballots had to be received by election night to be valid. Lawsuits seeking extensions were brought around the country for two reasons: a massive, pandemic-induced surge in mailed ballots, and concerns about the competence and integrity of the Postal Service, particularly after President Donald Trump appointed a major GOP donor as postmaster general.

The issue produced the Supreme Court's most controversial decision during the general election, prohibiting federal courts from extending ballot-receipt deadlines in state law.

Ample data is now available, providing perspective on what the actual effects of these deadlines turned out to be.

Perhaps surprisingly, the number of ballots that came in too late to be valid was extremely small — regardless of what deadline states used, or how much that deadline shifted. The numbers were nowhere close to what could have changed the outcome of any significant race.

Take Wisconsin and Minnesota, important states and sites of major court controversies on this topic. In both, voters might be predicted to be the most confused about the deadline for returning absentee ballots, because they kept changing.

Wisconsin law required absentee ballots to be returned by election night. A federal district court ordered that deadline extended six days. But the Supreme Court voted 5-3 to require the state's deadline to be respected.

Writing for the dissenters, Justice Elena Kagan invoked the district court's prediction that as many as 100,000 would lose their right to vote, through no fault of their own, if the normal deadline had to be followed. Commentators called this a "disastrous ruling" that "would likely disenfranchise tens of thousands" in this key state.

A post-election audit now provides perspective: Only 1,045 absentee ballots were rejected for failing to meet the deadline — 0.05% of the 1.9 million valid absentee votes cast, or 0.03% of the total vote. If we take it that President Biden won roughly 70% of the absentee vote nationwide, that means he would have added 418 to his margin of victory had these ballots been valid.

The fight in Minnesota was even more convoluted. If voters were going to be confused anywhere about these deadlines, with lots of ballots coming in too late as a result, it might have been expected there.

State law required ballots be returned by election night. But as a result of litigation, the secretary of state had agreed ballots would be valid if received up to seven days later. Just five days before the election, though, a federal court pulled the rug out from under Minnesota voters. It held the secretary of state had violated the Constitution and had no power to extend the deadline. The original deadline thus snapped back into effect at the very last minute.

But only 802 absentee ballots out of 1.9 million cast (0.04%) were rejected for coming in too late.

So, even though voting rights plaintiffs lost close to Election Day in both with the deadlines shifting back and forth, only a tiny number of ballots arrived too late.

But what about states that had a consistent policy throughout the run-up to the election that required ballots to be returned by election night? Among battlegrounds, Michigan provides an example. Only 3,328 ballots arrived after Election Day, too late to be counted, or 0.09% of the total.

Finally, in both Pennsylvania and North Carolina litigation did succeed in generating decisions that overrode state law and pushed ballot-receipt deadlines back.

These decisions provoked intense political firestorms in some quarters. The Pennsylvania Supreme Court's three-day extension became the primary justification that some Republican senators and representatives offered on Jan. 6 for objecting to counting the state's Electoral College votes.

But how many took advantage of these extensions? In North Carolina, according to information from the state Board of Elections, 2,484 ballots came in during the additional six days allowed — just 0.04% of the total valid votes.

The number was about 10,000 in Pennsylvania, out of 2.6 million absentee ballots — only 0.14% of the total there. These were not counted in the state's certified vote total. But had they been, Biden would likely have added around 5,000 votes to his winning margin, given that he won about three-quarters of the state's absentee vote.

These are not the numbers of ballots, of course, that would have come in late had the courts refused to extend the deadlines. They show the maximum number that arrived after Election Day, when voters had every right to return ballots this late. Even so, the totals are far lower than the 100,000 predicted in Wisconsin.

But had the statutory deadlines remained in place in Pennsylvania and North Carolina, there is no reason to think the number would have been much different from those in similar swing states like Michigan, where the statutory deadlines held and just 0.09% of ballots arrived too late.

These small numbers occurred despite a massive surge in absentee voting in nearly all states. What explains that?

Voters were highly engaged, as the turnout showed. They were particularly attuned to the risk of delays in the mail from seeing this problem occur in the primaries. Throughout the weeks before the election, voters were consistently returning absentee ballots at higher rates than in previous elections.

The communications efforts of the Biden campaign and the state Democratic parties, whose voters cast most of the absentee votes, got the message across about deadlines. Election officials did a good job of communicating these deadlines. In some states, drop boxes that permitted absentee ballots to be returned without using the mail might have helped minimize the number of late-arriving ballots, though we don't have any empirical analysis.

In a highly mobilized electorate, it turns out that specific ballot-return deadlines, and whether they shifted even late in the day, did not lead to large numbers of ballots coming in too late.

That's a tribute to voters, election officials, grass-roots groups — and to the campaigns.

Richard Pildes is a professor of constitutional law at New York University. He wrote this article for the Fulcrum, a nonprofit, nonpartisan news platform covering efforts to fix our governing systems. (It is a project of, but editorially independent from, Issue One.)