If you harvested the pods too early, they wouldn't be brown or cracked, The seeds would still be there, only they would be green. Sometimes the iris develop pods without seeds, My guess is that they got a bit of pollen material on the stigmatic lip, just enough to trigger the plant into making a pod, but not enough to fertilize the pod to make seeds. I may be wrong with this, but it's my hypothesis.
This video with Paul Black shows the technique for making crosses. It might be helpful for those wanting to give it a try.
https://www.bing.com/videos/se...
Somewhere on here are threads about hybridizing, maybe you could stroll through some older threads to find them. I know it's come up many many times over the years.
