Nana, the tree pictured in the thread I linked is in z8. It is at least 20 years old, so given that we just became z8 in the last 5 years, the tree was previously in z7b. With the changes in climate here, we're able to grow many things we couldn't grow previously. We've seen some extreme heat and cold swings throughout the year as a result also... which seems to have hardied up the trees and plants in our area quite a bit.
It was proposed in another thread that (it's suspected) that fig trees can "acclimate" to cold weather by one or two degrees (ºF) each year that they are in the ground. I don't recall if that was "with covering" or "without covering" or what, but it seems to hold true for most trees I've seen - if they can make it to the point that the tree trunk diameter is at least 7"-8", almost nothing can kill the damn things.