I think Hoppy's along the right lines too.
If memory serves, the CAA were also not happy with the ex PanAm aicrafts' stall warning system.
I believe that they used the stick shaker for high speed warning AND incipient stall and their point (the CAA) was that up in Coffin Corner the spread between the two wasn't that much.
Clawing my memory I believe the aircraft were also cleared to FL430 - but it was a long time ago.
Super move changing the digital autoflight system back to analogue.
Remember being on the ZE706 (corrosion trial) RAF acceptance flight test. What a mix up of APFDS that was (is?)
Anyway, I though vortex generators were to keep roll control in the event of a stall.
Stir the airflow and delay flow breakdown and so the ailerons would retain roll control.
Remember too the outboard ailerons are locked out with the flaps up anyway - are they unlocked with a stall warning - can\'t remember.
Must get my copy of Handling the Big Jets out of the loft!!