Where's the resin?

I've got Durban Poison and Haze females flowering for 4 weeks now. Only 1 DP is producing resin, the rest are coming up lame thus far. I had the same problem with White Widow where one of the three females didn't produce the medicine. Is it that the milage is varying? They are company seeds from BC Seedking and Amsterdam.
I'm suspicious of these seed companies. My Blueberries are doing great--but I propagated those seeds from company seeds.