I'm not entirely sure, but, with my shrimp I noticed that they dropped around 2 entire clutches when they were first put into the tank.
After a while they must have gotten used to the tank, which I had already cycled and what not prior to their introduction, and managed to hang onto their eggs until hatching.
I've noticed several times though that if the eggs become milky, or creamy as you describe, they will not hatch.
Only the eggs kept with the female remain healthy.
Once they get used to the tank and begin retaining their eggs until hatching they populate extremely fast.
My max population in a 10 gallon, with minimal food added, was around 250, just from their vigorous reproduction.