The Federal Aviation Administration (FAA) ordered 171 Boeing planes out of service after the 5 Jan incident.
It said it had finished 40 inspections but offered no further update on when the jets might be cleared to fly.
Airlines had said preliminary reviews revealed issues such as loose bolts.
Alaska Airlines and United, the two airlines with most of the affected planes, have had to cancel hundreds of flights since the planes were ordered out of service.
The FAA said on Wednesday that officials will review the findings to determine if the maintenance and inspection conducted on the first batch of planes is adequate.
Once that process has been approved, it will be required on every grounded plane before being cleared for flight, the agency said.
The update comes as pressure grows on Boeing and the FAA to answer for the emergency on the Alaska Airlines flight from Portland, Oregon to California, in which a cabin panel blew out shortly after take-off.
Passengers on the plane, which returned to the airport without serious injury, have filed two lawsuits. saying the incident led to intense fear and trauma and alleging that not all of the air masks on the flight were functioning.
“Mom … We’re in masks. I love you,” one passenger texted at the time, according to one of the complaints, which accuses Boeing and Alaska Airlines of negligence.
The FAA said last week that it was expanding its review of Boeing’s manufacturing processes and production lines, including for its troubled supplier Spirit Aerosystems.
It also said it would examine potential changes to the current controversial quality review system, in which the regulator delegates many of its responsibilities to Boeing staff, should be changed.
Senator Maria Cantwell, who represents Washington, the historic base of Boeing’s operations, last week sought documents from the agency, saying it appeared the FAA’s oversight processes had “not been effective in ensuring that Boeing produces airplanes that are in condition for safe operation”.
Boeing has been trying to repair its reputation since two of its 737 Max planes crashed in 2018 and 2019, killing 346 people.
Poor design of a piece of its flight control system was found to play a role, and authorities grounded its popular 737 Max planes globally for more than 18 months. Lax oversight by the FAA was also faulted.
Boeing has reported a string of smaller manufacturing issues as production resumed.
Boeing said this week that an outside party would be brought in to assess its production practices, with Boeing commercial airplanes president and CEO Stan Deal saying the company was “not where we need to be”.
