according to Mel Frank, who has written some books on the subject that are quite popular around here, the primary location for THC is going to be in the green bud itself (mostly in what are called brachts, which most people incorrectly refer to as calyx). According to him, resin is really not a large contributor to THC content, and is more of a form of self dense than anything. Likewise for crystals. He claims to have done the lab analysis to arrive at this conclusion.
I have smoked a lot, from north america, europe and asia (I consider myself a connoisseur), and though I prefer the taste of the buds covered in crystals, some of the most potent I've had didn't have a single crystal or look even slightly dusty. I tend to buy that crystals are not what you're looking for to determine the potency of your crop.
I think you mentioned that these were just seeds you got from random bags you smoked, so without a point of reference, I wouldn't go comparing your strain to anything else you see. There is so much genetic diversity out there. In general if the bag you got it from was potent, the chances are very high that what you grow will be potent.