“It is a vital government function that isn’t that hard to get right, so it’s at least a bit surprising to see errors today that you might think had been eliminated 20 years ago,” said David N. Rosen, a lawyer who was involved in a jury selection debacle in the early 1990s in Connecticut. “It counts as something that sounds hard to believe until you think a little more about it, and then it becomes all too easy to believe.”

In the Connecticut case, a truncated data field somehow identified all Hartford residents as dead, preventing them from being considered for federal juries. In Kent County, Mich., hundreds of thousands of people, many of them black, were not in contention for jury summonses in the early 2000s because a glitch led to only part of a master list being used to pick potential jurors. The Indiana Supreme Court in 2002 overturned a death sentence after “a flawed program” excluded nearly one-third of a county’s jury pool. And in the nation’s capital, a programming error once kept Washingtonians with misdemeanor convictions from jury duty.

“I think they probably happen more frequently than we know about, but it’s only rarely you can look out into the jury assembly room and say, ‘There’s something wrong right now,’” said Paula Hannaford-Agor, the director of the Center for Jury Studies, a project of the National Center for State Courts.

About 15 percent of Americans are called for jury duty each year, their ranks drawn from sources like rosters of licensed drivers and registered voters. With millions of names in the mix, a decentralized legal system, and harried judges, clerks and lawyers trying to stem backlogs, researchers and court officials said jury database errors can happen at plenty of points along the way.

There can be input errors, they said, or miscrafted algorithms. There can be software limitations, wrongly clicked buttons and stale data — all seemingly innocuous snafus that carry constitutional implications in a society where the courts have long grappled with how juries can, and cannot, be constructed. The courts have, for example, set down restrictions on lawyers using race or gender to exclude potential jurors.