I don't think you'd be able to take credit for a flap configuration change in demonstrating acceptable stall characteristics for certification, unless you actually automated it to be part of the pusher system somehow. Certainly I wouldn't try that with my authority!
I suspect it's simply that the L/D is still pretty good so the drag penalty isn't much worse than at zero, the AoA penalty seems to be small, and it also isn't too fast a translation for the flap, so by the time you get to flaps 15 you've dealt with the immediate AoA issue and it now gives you a bit more lift/margin to play with.