This coming April will be the 11th anniversary for me of installing most of my palms and other BLEs of varying hardiness.
I still give moderate protection to my Palmetto and Trachy -- both survivors from 2007. But my Needles and Minors get basically mulch and nothing else.
In terms of Arctic blasts and polar vortexes and the like, I've calmed down so much since '07. My feeling is what's gonna happen is gonna happen. It's fairly reasonable that most winters will bottom out between 0F and 5F. There is a slight, yet existential threat of -1F to -5F. And a very, very slight chance of something colder than that.
If winter damages or defoliates a tree, I have learned that the tree will come back, and within 2 years can completely recover (if winters are kind).
If winter outright kills a tree, I feel bad for the tree, but it is what it is. I have a very small property that is jam packed with too many plants. If winter claims a couple, I might just keep the space open or replace the lost plants with interesting, but non-marginal plants.