What I remembered is…Niantic told users they cannot reveal the probability of driftstone dropping after hunt. I think they will announce same words about materials drop rate.
Every time users posted the low drop rate issue of driftstone, every time Niantic replied “We cannot tell you the possibility of driftstone, but we have checked it and it’s normal.”
The word “normal” has no meanings because no actual possibility number, we don’t know what is “normal” or “abnormal.”