In the granite fabrication it was easy to tell. The wheel which was on a 4" angle grinder would bounce. I haven't started to do lapidary work yet but I'm sure like in the granite world its all about feel, also watching the pores close and seeing the scratchs disappear.
It depends on how you are carving your scales on the sc wheels. You are supposed to run the stone across the face of the wheel, using the whole face of the wheel. This can be done when cabbing a relatively small cab - but maybe not when you are grinding a larger piece, like a scale. Are you able to do that the way you are cutting them? If not then 2 or 3 times for one scale, may not be too many.
The stone starts to bounce very slightly and if you are grinding flat across the wheel (using the whole face of the wheel) with an 'edge' of the stone then you get chipout on the backside. So I dress it when the 'bounce' starts. I think more water may ease the onset of 'bounce'.