Well, knowing which ones are the males, or females, won't speed up breeding, in a group. Are yours mature? If so, have you noticed anything by way of potential breeding activity ? And if they are mature, do you try to condition them?
What are we assuming ?
From what I've heard ST's breed in much deeper water than most ST owners offer them. Haven't heard anything with IT's and breeding depth
The point is - it's just a matter of time, if a group is kept together, long-term, that visually sexing them really isn't important. If you only have one, and want to buy one more, then yes, obviously - like with Cichlids, but with lots of fish, it's just keeping a group long enough, which is what most people don't do, for a number of reasons, and thus, never giving the fish a chance to breed in the first place, since as you said, they may not be mature yet.
The depth aspect definitely could be a factor.