Yep, now you see the difference between north and south, e.g. Kiel is Zone 8a und Nürnberg 7a but we have now +11°C and Kiel -2°C.
On the other hand we can have in January -15°C but Kiel also, but maybe not so often.

So the USDA Maps are not made for exotic planting. And not made for Europe because we have a completely different climate than USA. Whole USA is more or less hot from April to November, not comparable to Middle and Northern Europe.
So even in South Carolina, Georgia and Texas frost up to -15°C can happen but in summer they are warmer than Rome. So maybe wine and some other agricultural things maybe planned by USDA Maps but not palm tree planting or so.