Having taken a hazmat course after high school, he called the Red Cross and was told they needed people like him. “I left my soon-to-be-ex-wife and 1-year-old son and went down,” he said. “I came back three days later,” after surviving on his own adrenaline, Little Debbie cakes handed out to volunteers and bottled water. After working for three days setting up a morgue, he was willing to go back, he said, but “they said we have trained people now, thank you very much for your service.”

After the attacks, Mr. Oliver said, his income dropped from about $300,000 a year to almost nothing. “This town kind of shut down musically,” he said. Then he began having back problems that have put him on crutches for the last five years, pain and depression, which wrecked his marriage and his ability to work, he said. As a volunteer, he feels marginalized.

“The police, the firemen — they got their thing,” he said.

As proof of service, he has his two-sentence Red Cross letter, another letter from a doctor he worked with at ground zero, some pictures he took and a handwritten pass. “If that isn’t enough, then....” he said forlornly, trailing off.

If Terry Graves’s experience is any guide, Mr. Oliver will need to have those letters redone. Ms. Graves worked as a volunteer Spanish-language interpreter after Sept. 11, according to letters from two people who remembered seeing her at the Federal Emergency Management Agency’s Disaster Assistance Service Center on Worth Street. Ms. Graves used the letters to qualify for workers’ compensation, but the Sept. 11 fund bounced them back, saying they would accept only original sworn documents.

Her letters were written in 2007, and one signatory has since moved out of New York. “I don’t think I’m going to get this money,” she said. “By the time you prove it, you’re going to be dead.”

She also has a copy of a FEMA badge with her photograph on it. “I couldn’t come up with another witness if I tried,” she said. “I wasn’t there to socialize; I was there to do a job.”

Mr. Hazan, 41, used his expired Rockland County emergency medical technician’s card to wheedle his way past police lines to ground zero on Sept. 12, 2001.