In 2013, NYC investigators posed as 63 ineligible voters, ALL BUT ONE allowed to vote, that one where someone tried to be son of poll worker

The one case where a fraudulent voter was stopped from voting was when the fraudulent voter tried to be the son of the poll worker.  From the WSJ (emphasis added):

. . . In 2013 the New York City Department of Investigation—the storied law-enforcement arm of city government, which houses and manages all the city’s inspectors general and investigators—decided to test the system. City investigators posed as 63 ineligible individuals still on the city voter rolls. Each ineligible voter had died, moved out of the jurisdiction, or been convicted of a felony at least two years earlier. 

The investigators didn’t go to great lengths to hide their attempted fraudulent votes. In five instances investigators in their 20s or 30s posed as voters age 82 to 94. In some cases the investigators were of different ethnic backgrounds from the voters they were impersonating. Yet each was given a ballot and allowed to cast a vote without question. 

 In other instances the investigators informed the poll worker that they had moved but didn’t have time to get to their new home on Election Day; all but one was allowed to vote. Only one investigator was flat-out rejected. He had the misfortune of trying to vote at a polling place where the clerk was the mother of the ineligible felon he was impersonating.  

Ninety-seven percent of the barely disguised phony voters were allowed to vote unimpeded, and none was referred for criminal charges or officially reported to the Board of Elections. One can only imagine what a sharp operator trying to fix an election could do by flooding polling places with ineligible voters. . . .