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Every year on Sept. 11, relatives and friends of people killed at the World Trade Center return to the memorial that fills the footprints of the towers. The mayor, even presidential candidates, have joined them as the victims’ names are read. Many run their fingers over some of the thousands of names etched in bronze and wedge stems of flowers into the letters.

But there is another anniversary related to the attacks, one that often receives far less attention: May 30, the day in 2002 when the cleanup of ground zero officially concluded with a modest ceremony.

This year was different. On Thursday, a crowd of families, friends and survivors with ties to a segment of victims that continues to grow gathered under a canopy of fog as the 9/11 Memorial and Museum in New York City dedicated an addition called the Memorial Glade. It is meant to acknowledge the ever-extending tendrils of the tragedy, recognizing the people — largely rescue and recovery workers — whose illnesses and deaths came years after the towers collapsed.

“The story of 9/11 is only half written,” said Rob Serra, 39, who was a rookie with the New York City Fire Department when he worked at ground zero.