Boeing737,
It's over 20 years ago, testing my memory a bit, but the Australian Authority (CASA's predecessor) were not satisfied that Airbus had adequately demonstrated the stall, and required further tests. No stall to their satisfaction could be demonstrated, simply a minimum achievable speed, the 'Z' speed, with incomplete airflow separation.
I stand correction in detail, but that's the basic history.
Regards,
Old Smokey