Keith, I think hardiness is an innate characteristic of a species, acquired over centuries, if not, millenia, and not likely to change quickly. Believe it or not, ears of corn used to be only about an inch or two, long. However, over centuries of Native Americans selecting the seeds from the "biggest" ears, each year, to plant the next year, corn ears eventually evolved to be the size they are today...but it took centuries.
I think what usually changes, is that a plant, once thought to be more tender, proves to be hardier in a colder zone. There are some plants, for instance, that once existed in a broader area (that included more zones), than it does now, but became rare in places where it used to occupy, due to human habitat destruction, deforestation, plant diseases, etc.
I think this may be true of say, longleaf pines, which has more recently been shown to be hardier, than z7, or only in the SE, simply because it is virtually seen, only, in the South (even though it now occupies less area, even in the SE, than it once did, due to things like deforestation). Its range may have been larger, or the climates in the north and south more similar, at points in antiquity.
I grow several plants, that contain a southern state, in its common name, that has proven hardy, here, with NO PROTECTION. Yet, local nurseries don't carry these plants, simply because they are believed to be too tender to grow, here.

Since Florida is only subtropical, and not actually in the tropics, many tropical palms grown there, get damaged, when temps go below the palms "native/innate" comfort level. Some Sabals, and needles are native to Florida. Other palms types are not native there, and often suffer damage, when factors of climate, become different from what is that plant's DNA.

So, I don't think a palm grown in Florida is less hardy, elsewhere. I believe hardiness is in a plant's DNA, and plant or animal, would take a very long time to change. Like the YouTube video I posted of South Floridians, in February, distraught over the damage to their TROPICAL fruit trees, after 23 degrees, wouldn't make any difference if the same tropical fruit tree experienced the same 23 degrees, in a northern place. It may only recover, with a shorter cold spell, in the warmer zone, but the initial damage would affect the plant, whether it recovers or not.