When one is trying to breed Corydoras, a special breeding tank will usually give better results than waiting for them to spawn in the community tank. Even if they do spawn in the community tank, it is very likely you will not notice it at all.
The eggs are well hidden by the fish, and even if the eggs survive the hungry attentions of the co-inhabitants of the tank and the parents themselves, the larvae coming out of the egg are extremely vulnerable. The first thing they have to do when emerging from the egg is to go up for air to fill the swim bladder. Still, some may occasionally survive this, and after a month or three the owner will be in for a surprise when the first 2 cm long juvenile calmly cruises the tank for food.