Perhaps something parallel may help? Ralph Moore raised Crested Jewel and Crested Sweetheart from Little Darling X Crested Moss. Crested Jewel is much more fertile than Sweetheart. He grew a large plant of Crested Sweetheart for decades and eventually it produced a more fertile sport which set quite a few hips. Paul Barden worked with that sport for some time and reported virtually nothing resulted from it. I would suggest perhaps reports of breeding were made possible by potential mutations. I would further suggest climate more likely provided more opportunities. I have observed significant differences in fertility in roses due to climate. Rosarium Uetersen in high heat, has no sexual parts, only petals and petaloids resulting in dense pompon type flowers. Grow it in a cooler, damper climate such as near the coast and it becomes a semi double flower with a center full of stamen and anthers. Iceberg sets few self hips in the high inland valley temps, but closer to the cooler coast, it sets large hips from nearly every bloom. Mermaid sets no hips in hot inland valleys, but will occasionally set hips with one or two seeds in the cool, damp coastal environment. I'm sure there are many other examples of fertility variations due to temperature and humidity differences but these few come readily to mind from my own observations. This photo of the more fertile Crested Sweetheart mutation has been on the Crested Sweetheart rose page since I posted it there in March of 2010.