On the rubbing, you can tell when the females are getting inseminated while that happens. Watch it really close - the male aims his gondopodium into the female. I caught this on tape. The males have directional control on that straight anal fin, so they swim up right next to the female and point it right into her and BAM. Fishy love making.
I also caught my Molly on tape dropping her first batch of fry, other than that, I caught my Swordtail dropping the end of her last batch (mostly dead) but didn't pull out the camera for that one, all the live ones came out first and I missed those.
It happens at random times for me, but yeah, I always come into the room and there they are...