Officials said the 9-1-1 operator typed in the wrong address while taking the call.
"This is another example of a $1 billion project not working properly," said Leroy McGinnis of the UFA. "Had units arrived on scene in their order, we may not have saved all the lives, however we'll never know because we didn't get the chance."
Firefighters arrived Saturday morning at the Woodside house to find it illegally divided into apartments.
The aftermath has already caused a ripple effect in the neighborhood.
Shortly after firefighters vacated the victims, the Buildings Department slapped a vacate order on the premises, citing multiple violations - including an illegal apartment downstairs where victims were found.
"One was right at the entrance to the front door; one was in the bedroom, appeared to be trying to get out of the basement window, was right under the window; and another one was right in the middle," FDNY Chief Vin Mavaro said.
As neighbors mourned the victims, at least some of whom were said to be members of the local Bangladeshi community, others in the diverse community complained that too many homes there have been illegally subdivided, causing dangerous conditions.
"Everybody changes from two-family to four, five, six families - it's not right," one neighbor said. "I pay my tax for two families - why should I pay the same as they pay?"
Just next door, inspectors found more illegal apartments, and another building was ordered shut, leaving several people homeless.
"I was told I had to vacate," one resident, Jeffrey, said.
He said he lived in a single-room occupancy in the basement for several years.
"I assumed everything was legitimate," Jeffrey said. "When I was on Welfare, inspectors came and inspected it. They were paying the rent."
Investigators will have their hands full. Perhaps most ominously, in the building with the fire, the violations included the absence of a second exit from the basement - from which some of the victims might have been able to escape.
At this point, any role that the building violations might have had in causing the fire or preventing the victims' escape remains under investigation.
CBS 2's John Metaxas contributed to this report.