I think your right and I also think they are laying them when I'm not around and by the time I am around the #40## platies and guppies have had a sneaky snack.
I was at my lfs this afternoon and was chatting to one of the staff members about cories and how I was trying to breed them and he suggested getting an identical tank to the one I have now and making a copy and putting the cories in there on their own to see what happens then .... he then said that cories grow huge (held his fingers about 12 inches apart) and can live for 25 years .... I then began to wonder if he was bulls****ing me. I'm pretty certain cories have around a 5 year lifespan and 12 inches long??? um ... I hope not!!