How soon can you determine select plants when flowered from clone?

A quick question. Cloned a few strains about 3 weeks ago from an outdoor medical grw op. They were already triggered and were barely showing pistils but they were there. Put them in 12/12 and now there is deffinately new growth and leaves and they are rootbound in the oasis tray that I cloned them in. Ive been using azatrol to fight fungus gnat larva and flies and it seems they continue to eat roots and show up. There is new growth on the roots however.
So my question: none of the clones seem to show any resin formation yet they have been in 12/12 for 3-4 weeks and are showing flowers with small sugar leaves, yet there is no resin. Does that mean those strains are not going to be that great of weed? I had somone saying its the stress causing this, but how does stress delay trichome formation? Shouldnt I be able to tell which clone is going to be the best after so many weeks in flower? My other plants show resin on large fan leaves by 2 weeks.

Sorry if this seems like a dumb question. I got into a little debate with somone over it.

Its primarily a genetics thing.. Stress would affect actual growth, not resin production.. Its still potentially great weed, there really isn't anyway to know about a mystery plant much earlier than harvest beyond aroma.. Its not even really about how much resin/crystal there is, as much as whats inside, and that won't be ideal until full maturity..

Good point. Couldnt agree more. But my past experiences are if I dont see resin by the 3rd week then the genitics turn out to be garbage. I had that experience with grapefruit kush from a club, dutch passion orange bud (out of 6 fems only one pheno worth keeping) and DP purple #1, completely purple and no visable trichomes. Both Toatally shit weed. But you bring up the real point which truly is that you really dont know untill a 30 day jar cure.