Boeing personnel were authorized to work on behalf of the FAA. Tasks were divided up. As the MCAS was tweaked on simulators, the engineers adjusted the maximum rotation of the stabilizer. Most engineers thought it was 0.6 degrees. Turns out, MCAS had been set up to be able to move the stabilizer 2.5 degrees each time. It was also authorized to actuate multiple times.
That info was not included in the System Safety Analysis submitted for the MAX's final approval. IIRC, it's supposed to include everything that is changed.
"After the Lion Air Flight 610 crash, Boeing for the first time provided to airlines details about MCAS. Boeing’s bulletin to the airlines stated that the limit of MCAS’s command was 2.5 degrees.
That number was new to FAA engineers who had seen 0.6 degrees in the safety assessment.
The FAA believed the airplane was designed to the 0.6 limit, and that’s what the foreign regulatory authorities thought, too,” said an FAA engineer. “It makes a difference in your assessment of the hazard involved.”
https://www.seattletimes.com/business/boeing-aerospace/failed-certification-faa-missed-safety-issues-in-the-737-max-system-implicated-in-the-lion-air-crash/