You're misinterpreting the significance of stall warning
By rules .. the "Stall Warning" must activate near the point that the aircraft will stall .. and continue if the aircraft (for any reasons) go in the stall mode
The stall warning must continue .. until the aircraft is no more stalled or no more near of the stall mode
By Airbus design the AF447 stall warning stopped when the aircraft was in stall ..
BEA notice in conclusions that this is a contributing factor for the accident