What?! You mean there is no tooth fairy?!
Lu, as you said, the advancing blade is flapping down with respect to the horizontal when you're in forward flight.
However, as I said, flapback alters the path that the blades would otherwise follow, so the 'maximum rate of flapping up' mentioned above is with respect to the original, 'unflapped' tip path.
Regarding your comment about retreating blade stall; yes, the advancing blade will be producing high lift, but as the name implies, blade stall is all about stalling, and the subsequent loss of lift;
i.e. the retreating blade loses so much airspeed due to your high forward speed, and is already at a high angle of attack because of the power and blade pitch you have in to maintain that speed that it stalls like any other wing, loses a good degree of its lift, and there you have it.