Maurice - what you wrote is really starting to make total sense to me.
That makes sense that it is more about crossing southern bred with northern bred cultivars to produce intros that may often grow well in different climates.
It doesn't impact the seedling as to where it was originally sown and grown? It is more about pedigree genetics, correct? I ask that question because I have received plants as well as seeds from a northern zone (not dayliles) but other plants like Brugmansias, salvia, and herbs. The seed grown plants seemed to tolerate the heat a bit better. I assumed that was because the heat tolerant seed grown plants were the seedling survivors and the other seeds didn't. So the toughest seeds went on to produce plants that grew and survived better than a plant or less heat tolerant seed did here in my garden.
I am getting over the misconception that all daylilies are tough and can grow anywhere. That couldn't be further from the truth apparently.
