Brooklyn has lost 9,800 rent-stabilized apartments since 2020, more than any other borough, according to an analysis released Friday by the Housing Data Collaborative, a nonprofit research group that cross-referenced state registration rolls with city property records.

The losses are concentrated where the pressure is highest. Bushwick accounts for roughly 2,100 vanished units and Crown Heights another 1,700, with the report flagging a pattern of buildings that simply stop registering units year over year without any legal basis for deregulation appearing in the record.

"Units don't fall out of stabilization anymore; the law mostly closed those doors in 2019," said Yesenia Cruz, an organizer with a Bushwick tenant union who reviewed the findings. "What we're looking at is quiet noncompliance. A unit that isn't registered is a unit that's very hard to fight for."

State housing officials said registration enforcement has increased, citing 340 Brooklyn buildings brought back into compliance last year, but acknowledged the agency relies heavily on tenant complaints to find problems.

The report recommends automated cross-checks between registration data and advertised listings, a fix its authors describe as "unglamorous, cheap, and overdue." A public version of the underlying database, searchable by address, is scheduled to go online in September.