Please take what I am about to say as with a very large dose of skepticism and distrust. That last photo you post does very much look like a preflower of the female variety. HOW EVER it very well could be a think stipule, I.E a small straight flat leaf found at the base of each branch. Though it does very much look like a preflower to me*..
But please, please, please dont quote me on that. its really way to early to tell with any thing beyond a 34.487% certainty.
Edit: I also wanted to say I really like your set up, simple but loaded with potential! Beautiful ladies as well keep up the good work!
Here is a photo I took from one of my current ladies when she first started to show preflowers.
the preflower is right next to the branch, the big green thing in front of it is one of the stipules I mentioned in the other post. Its not the best photo but I hope it helps. though really nothing will ease your mind till it actually pops pistils which if that is a preflower is still several days away.