It certainly makes more sense to look at all the data, not just extreme cold temps. It is definatly a California outfit though. They have me, in West Central Texas, having the same climate as Deep East Texas. Trust me they are not the same! For one thing they have trees. Maybe we could get the Aggies to do something similar for Tx, OK, and LA.
I put a comments on one of the other threads about my disappointment with the accuracy of the zones in the Austin area. They don't have enough distinction in rainfall or soil type in the east. Maybe that works OK in the deep south but not in TX. Abilene and San Angelo don't belong in the same zone as Nashville, that's for sure. Do you think zone 10 is correct for your area?
When looking at USDA zone recommendations for a new plant or variety, I dont buy anything that isn't OK for zone 9 even though we are officially in zone 8. If it can't take the heat of zone 9 or lack of winter chill there, I don't want to try it. We have an expression here about native TX plants - they take the heat and the sleet.